# Interplay between local moment and itinerant magnetism in the layered
metallic antiferromagnet TaFe1.14Te3

Sae Young Han  Department of Chemistry, Columbia University, New York, NY, USA
Evan J. Telford<EMAIL_ADDRESS>Department of Chemistry, Columbia
University, New York, NY, USA  Department of Physics, Columbia University, New
York, NY, USA  Asish K. Kundu  Condensed Matter Physics and Materials Science
Department, Brookhaven National Laboratory, Upton, NY, USA  Sylvia J. Bintrim
Department of Chemistry, Columbia University, New York, NY, USA  Simon Turkel
Department of Physics, Columbia University, New York, NY, USA  Ren A. Wiscons
Department of Chemistry, Columbia University, New York, NY, USA  Department of
Chemistry, Amherst College, Amherst, MA, USA  Amirali Zangiabadi  Department
of Applied Physics and Applied Mathematics, Columbia University, New York, NY,
USA  Eun-Sang Choi  National High Magnetic Field Laboratory, Tallahassee, FL,
USA  Tai-De Li  Nanoscience Initiative at Advanced Science Research Center,
Graduate Center of the City University of New York, New York, NY, USA
Department of Physics, City College of New York, City University of New York,
New York, NY, USA  Michael L. Steigerwald  Department of Chemistry, Columbia
University, New York, NY, USA  Timothy C. Berkelbach  Department of Chemistry,
Columbia University, New York, NY, USA  Abhay N. Pasupathy  Condensed Matter
Physics and Materials Science Department, Brookhaven National Laboratory,
Upton, NY, USA  Cory R. Dean  Department of Physics, Columbia University, New
York, NY, USA  Colin Nuckolls  Department of Chemistry, Columbia University,
New York, NY, USA  Xavier Roy<EMAIL_ADDRESS>Department of Chemistry,
Columbia University, New York, NY, USA

###### Abstract

Two-dimensional (2D) antiferromagnets have garnered considerable interest for
the next generation of functional spintronics. However, many available bulk
materials from which 2D antiferromagnets are isolated are limited by their
sensitivity to air, low ordering temperatures, and insulating transport
properties. TaFe1+yTe3 offers unique opportunities to address these challenges
with increased air stability, metallic transport properties, and robust
antiferromagnetic order. Here we synthesize TaFe1+yTe3 (y = 0.14), identify
its structural, magnetic, and electronic properties, and elucidate the
relationships between them. Axial-dependent high-field magnetization
measurements on TaFe1.14Te3 reveal saturation magnetic fields ranging between
27-30 T with a saturation magnetic moment between 2.05-2.12 µB.
Magnetotransport measurements confirm TaFe1.14Te3 is metallic with strong
coupling between magnetic order and electronic transport. Angle-resolved
photoemission spectroscopy measurements across the magnetic transition uncover
a complex interplay between itinerant electrons and local magnetic moments
that drives the magnetic transition. We further demonstrate the ability to
isolate few-layer sheets of TaFe1.14Te3 through mechanical exfoliation,
establishing TaFe1.14Te3 as a potential platform for two-dimensional
spintronics based on metallic layered antiferromagnets.

van der Waals materials, magnetic metals, layered antiferromagnetism,
magnetotransport, high-field magnetic susceptibility, angle-resolved
photoemission spectroscopy.

##  Introduction

Identifying candidate low-dimensional materials combining metallic transport
behavior with robust antiferromagnetic order is crucial to advancing spin-
based nanotechnologies. Van der Waals (vdW) magnets, in particular, provide an
ideal platform for fabricating atomically-thin spintronics and magneto-optic
devices[1, 2, 3, 4, 5], as they possess diverse magnetic phases and electronic
properties that persist down to the two-dimensional (2D) limit. Within this
family of materials, those exhibiting metallic electronic transport have
received intense attention due to their potential functionality as spin
injectors[6, 7], magnetic tunnel junction electrodes[8], or spin-orbit torque
devices[9, 10]. Among the available 2D magnets, layered antiferromagnets are
exceptionally attractive due to the increased resilience to external magnetic
fields[11, 12], sensitivity of electrical resistance to field-induced
antiferromagnetic-to-ferromagnetic transitions[13, 14], faster spin
dynamics[15], utility in high-frequency spin-orbit torque experiments[16], and
capability for higher packing density than ferromagnets in memory storage
devices due to the absence of stray fields[17]. Despite an obvious need, vdW
materials integrating metallic behavior with layered antiferromagnetic order
are notably scarce[18]. TaFe1+yTe3[19, 20, 21, 22] is one candidate to
overcome many existing limitations of vdW magnets, boasting a high Néel
temperature ranging between 160 and 200 K[19, 21, 23, 24, 25], metallic charge
transport properties[19, 23, 24, 26, 27], and stability under ambient
conditions, showcasing its promise for metallic antiferromagnet-based
spintronics. However, a comprehensive understanding of the magnetic and
electronic properties of TaFe1+yTe3 has yet to be achieved.

Figure 1:  Structure and composition of TaFe1.14Te3. A) Crystal structure of
TaFe1.14Te3 viewed along the crystallographic b-axis. Morphological long in-
plane (LIP) (green), short in-plane (SIP) (red), and out-of-plane (OOP) (blue)
directions are shown relative to the crystallographic a, b, and c-axes. B)
Crystal structure of TaFe1.14Te3 viewed along the crystallographic b-axis with
the orientation of the Fe1 (orange arrows) and Fe2 (purple arrows) magnetic
moments in the antiferromagnetic state overlayed. C) Crystal structure of
TaFe1.14Te3 viewed along a direction that clearly displays the Fe1/Fe2 chain
structure. The Te atoms are removed for clarity. D) False-colored optical
microscope image of a TaFe1.14Te3 flake exfoliated onto polydimethylsiloxane
(PDMS). The corresponding layer numbers for different regions were determined
by atomic force microscopy and optical contrast (Fig. S1). E-G) Ta (E), Fe
(F), and Te (G) elemental maps of a single crystal of TaFe1.14Te3 as
determined by SEM/EDX. The lower right inset of each elemental map gives the
corresponding elemental composition normalized to Te. In (E) and (F), the
error bars represent the standard deviation of multiple measurements between
various crystals and growth batches.

In this work, we synthesize TaFe1+yTe3 (y = 0.14) and explore its electronic
and magnetic properties, uncovering its potential for atomic-scale spintronic
devices based on vdW materials. Temperature- and magnetic-field-dependent
magnetization measurements reveal a paramagnetic (paramagnetic)-to-
antiferromagnetic transition at 164 K followed by a transition into a spin-
glassy magnetic phase below $\approx$100 K. At liquid helium temperature, full
magnetization saturation occurs only at 27-30 T for all morphological
directions with a saturation magnetization moment of 2.05-2.12 µB. Through
density functional theory (DFT) calculations, we confirm the stability of the
metallic antiferromagnetic phase and characterize its electronic structure.
Longitudinal magnetotransport and Hall measurements verify the metallic nature
and demonstrate a strong coupling between magnetic order and electronic
transport. Angle-resolved photoemission spectroscopy (ARPES) measurements
further support the metallic nature of TaFe1.14Te3 and reveal a complex
interplay between local moment and itinerant magnetism. We also demonstrate
the ability to isolate few-layer flakes of TaFe1.14Te3 through mechanical
exfoliation, solidifying its practicality for spintronic applications.

##  Results and Discussion

Single crystals of TaFe1.14Te3 are grown using the chemical vapor transport
method (see methods for full details). Tantalum, iron, tellurium, and TeCl4
powders are pressed into a pellet, and sealed in a fused silica tube under
vacuum. After seven days in a temperature gradient of 700°C to 600°C, needle-
like crystals are obtained in the sink side of the tube. We performed single
crystal X-ray diffraction (SCXRD) to determine the structure (Fig. 1A-C). The
low-dimensional layered telluride TaFe1.14Te3 crystallizes in the P21/m space
group. The structure features Ta-Fe1-Fe1-Ta ribbons aligned along the b-axis
while sandwiched between Te layers. Along the ribbon, the Ta atoms are
octahedrally coordinated by six Te atoms, and the Fe1 atoms, which make a one-
dimensional zig-zag chain, are tetrahedrally coordinated by four Te atoms.
Unlike the Fe1 site, the Fe2 site is partially occupied, and the Fe2 atom
nestles in the center of the square pyramid formed by Te atoms (Fig. 1A).
Single crystals are stable under ambient conditions and the layered nature of
the structure and corresponding interlayer vdW bonds allows for the isolation
of air-stable few-layer flakes of TaFe1.14Te3 through mechanical exfoliation
down to the monolayer limit (Fig. 1D). Corresponding tapping-mode atomic force
microscopy images of an exfoliated sample can be found in Fig. S1. Previously
reported neutron diffraction measurements on TaFe1+yTe3 determined that the
magnetic moments are localized on the Fe atoms and that the magnetic structure
is A-type antiferromagnetic with Fe1 spins within each layer coupling
ferromagnetically while Fe1 spins between the layers couple
antiferromagnetically[23]. The Fe2 spins within each layer align parallel with
Fe1 spins (Fig. 1B). The atomic ratio of different constituent elements was
determined through SCXRD occupancy refinement (Tab. S1) and confirmed by
energy dispersive X-ray spectroscopy (EDX) on freshly cleaved samples (Tab.
S2). Corresponding scanning electron microscopy (SEM)/EDX elemental maps of a
TaFe1.14Te3 single crystal for Ta, Fe, and Te with each collection normalized
to Te demonstrate that there is no evidence of Fe clustering down to the
micron scale (Fig. 1E-G).

Since the Fe2 site is only partially occupied, we first characterize the
uniformity of the Fe2 distribution and the impact of Fe2 on the local
electronic properties. We performed scanning tunneling microscopy (STM) and
spectroscopy (STS) on cleaved bulk TaFe1.14Te3. In Fig. 2A, we present an
atomically-resolved STM image of the vdW plane at 7.5 K. The selected
distances determined by a fast Fourier transform (FFT) of the real-space STM
topography are Te $\cdots$ Te (nearest neighbor) = 0.35, 0.36 nm, Fe2 $\cdots$
Te = 0.52 nm, and Te $\cdots$ Te (next nearest neighbor) = 1.01 nm (Fig. 2B),
in good agreement with those obtained from SCXRD (Fig. 1A). With its atomic
precision, STM allows us to view the topographical corrugation of the Fe
chains in detail. We observe an inhomogeneity of the intensity in the image,
which may indicate random nanometer-scale clustering of Fe2 in the crystal, as
previously hypothesized in a Mössbauer spectroscopy study of TaFe1+yTe3[20].
Corresponding STS measurements show a metallic-like density of states (DOS) at
all points across multiple Fe chains, revealing that the occupancy of the Fe2
site does not significantly impact the local electronic structure (Fig. S2).

Figure 2:  Atomic-scale characterization of TaFe1.14Te3. A) STM image of
TaFe1.14Te3 cleaved along the vdW gap. The image was obtained at T = 7.5 K in
constant current mode (Vb = 400 mV, I = 50 pA). B) Corresponding FFT of the
STM image. Select periodicities are denoted by dashed white circles. C) TEM
micrograph of an exfoliated TaFe1.14Te3 flake with a thickness $<$ 50 nm
viewed along the OOP direction. D) Corresponding electron diffraction image of
the same flake in (C). Select d-spacings are denoted by solid black bars. In
all panels, the orientation of the images with respect to the morphological
SIP and LIP directions is given in the lower left inset.

To confirm that the quasi-one-dimensional nature of the structure persists in
exfoliated flakes, we performed transmission electron microscopy (TEM) and
corresponding selected-area electron diffraction (SAED) measurements on an
exfoliated flake of TaFe1.14Te3 with a thickness $<$ 50 nm (Fig. 2C, D; see
methods for details). The diffraction pattern shows that the crystallinity is
intact in the exfoliated flake of TaFe1.14Te3. This is also seen in the real-
space image, in which we observe distinct lines of atoms along the direction
of the chains as depicted in Fig. 1C. Select atomic distances from the SAED
image are 0.17 nm for the close-range Fe atoms and 0.94 nm for the interchain
Fe atoms (Fig. 2D), in good agreement with those obtained from SCXRD (Tab. S1
and Fig. 1A, B) and STM (Fig. 2A, B).

Figure 3:  High-field magnetic properties of TaFe1.14Te3. A) versus T for H
oriented along the SIP (solid green lines), LIP (solid blue lines), and OOP
(solid red lines) directions. Both zero-field-cooled (ZFC) and field-cooled
(FC) traces are shown. All traces were collected with a field of H = 0.1 T.
The extracted Néel temperature is shown by a black dashed line. Layered
antiferromagnetic and paramagnetic phases are denoted by grey and white
regions, respectively. The inset shows inverse versus T for H oriented along
the SIP (solid green line), LIP (solid blue line), and OOP (solid red line)
directions. Dashed black lines are linear fits to each trace. The extracted w
and µeff are given in the upper left and lower right insets, respectively.
B-D) M versus H at different Ts for H oriented along the OOP (B), LIP (C), and
SIP (D) directions. In each plot, the extracted saturation magnetization
(Msat) and Hsat are given in the inset. Note that because both the OOP and SIP
directions contain a component parallel to the Fe1/Fe2 spin directions, they
both exhibit metamagnetic transitions. The LIP direction, however, is
completely perpendicular to the Fe1/Fe2 spin directions and only displays a
gradual spin-canting process.

We measured the magnetic susceptibility () of TaFe1.14Te3 as a function of
magnetic field (H) and temperature (T). In Fig. 3A, we present vs. T curves
with H along the SIP, LIP, and OOP morphological directions (see Fig. 1A for
reference to crystallographic axes). When cooling the sample from room
temperature, the measurements show a paramagnetic-to-antiferromagnetic phase
transition, characterized by a peak in at the Néel temperature TN = 164 $\pm$
2 K (Fig. S3, S4 for additional data). The Néel temperature is also confirmed
through H-dependent heat capacity measurements (Fig. S5). Below the Néel
temperature, the zero-field-cooled (ZFC) and field-cooled (FC) branches
separate, signaling the emergence of a spin-glassy phase below $\approx$100 K
(Fig. S6-S9 for a more detailed analysis)[25]. This behavior, often associated
with competing antiferromagnetic and ferromagnetic interactions, has been
observed in other TaFe1+yTe3 stoichiometries[25] and certain FexMn1–xTiO3
systems where long-range antiferromagnetic and re-entrant spin-glass phases
can coexist[28, 29, 30, 31]. The extracted Weiss temperatures (w) in the
paramagnetic phase convey strong ferromagnetic coupling, with values of 154 K,
158 K, and 149 K for the OOP, LIP, and SIP directions, respectively (inset of
Fig. 3A). The Curie-Weiss fit estimates an effective magnetic moment (µeff)
ranging between 4.26-4.28 µB for all morphological directions, in line with
the expected local moment of 4 µB for a majority high-spin tetrahedral Fe2+
ion (Fig. S23)[32].

Fig. 3B-D plots the magnetization (M) vs. applied H along all morphological
directions (see Fig. 1A) up to 35 T at various T. The OOP- and SIP-oriented M
vs. H curves at 1.5 K reveal a series of steps in M between 9-15 T after which
M continues to increase until saturating at 29 T and 30 T, respectively (Fig.
3B, D, and Fig. S10). The exact nature of these steps is unclear without
further measurements of the high-field magnetic structure, but are likely due
to metamagnetic transitions (see Fig. S11 and S12 for additional data). The
LIP-oriented M vs. H curve at 1.5 K is linear up to 27 T after which it
saturates, indicating a gradual spin canting process (Fig. 3C). This confirms
the LIP direction as the hard axis (Fig. 3C and Fig. S10). At 1.5 K, the
sample reaches a saturation magnetic moment for all axial orientations ranging
between 2.05-2.12 µB, which is significantly smaller than the µeff determined
for the high-T paramagnetic phase. As expected, increasing T decreases the
saturation magnetic moment and the H value at which the moment saturates.

Figure 4:  Electronic transport properties of TaFe1.14Te3. A) (left) and d/dT
(right) versus T at zero H. The extracted residual resistivity ratio (RRR =
R(300K)/R(2K)) is given in the inset. The extracted TN is shown by a black
dashed line. B) M versus H at 1.5 K for H parallel to the OOP direction. C)
RHall versus H above (solid yellow line) and below (solid magenta line) TN.
Two distinct linear regions (denoted by dashed black lines) are observed below
TN, whereas a single linear region is observed above TN. Additional traces at
different temperatures can be found in Fig. S18. An optical image of the
device is given in the inset. D) Magnetoresistance ratio, MRR =
[(R(H)-R(H=0))/R(H=0)]$\times$100, versus H at various T for fields parallel
to the OOP direction. Both forward and backward traces are shown. The T at
which each trace was taken is given in the inset. The dashed black line
denotes the 1.5 K metamagnetic transition.

Our measured saturation moments of $\approx$2 µB are consistent with those
assigned previously based on neutron diffraction measurements of the
antiferromagnetic phase[23]. The discrepancy between µeff and the measured
saturation magnetic moment implies that both local moment and itinerant
magnetism coexist in TaFe1.14Te3. For further insight, we performed first-
principles DFT calculations on TaFe1+yTe3 with y = 0, 0.25, and 1 with various
magnetic orderings (see methods for details). We find that the
antiferromagnetic order shown in Fig. 1B, with intraplane ferromagnetic order
and interplane antiferromagnetic order, is always electronically stable and
typically lower in energy than other magnetic orderings (including non-
magnetic), although the energy differences are often times small. Löwdin
charge analysis of Fe atoms gives a positive charge of 0.3-0.5 and a magnetic
moment of 2.2-2.4 µB, for both Fe1 and Fe2 (Tab. S3), in good agreement with
our measured saturation moment. Because DFT with common functionals is not
appropriate for strongly correlated electrons, the agreement with experiment
supports the picture that electron itinerancy is responsible for the
suppression of the magnetic moment. Although the character of the bands near
the Fermi energy (EF) is found to be a complex and nearly equal mixture of Fe
3d, Ta 5d and Te 5p orbitals (Fig. S20,S21), all DFT calculations predict a
metallic electronic structure, whose properties we study further by
magnetotransport measurements.

In Fig. 4, we report the magnetotransport of TaFe1.14Te3 single crystals.
Transport devices were fabricated using a micro-soldering technique which
consists of drawing micron-scale contacts with Field’s metal using a
micromanipulator (see methods for details)[33, 34]. Fig. 4A plots the zero-
field resistivity () of TaFe1.14Te3 versus T. Overall metallic behavior is
observed with decreasing with decreasing T. At T = 175 $\pm$ 3 K, there is a
sharp jump in the derivative of versus T, which is attributed to the onset of
antiferromagnetic order. Below this temperature varies approximately as T2,
saturating to a constant value at low T.

Fig. 4D presents the H dependence of the magnetoresistance ratio (MRR). MRR is
defined as MRR = [(R(H)-R(H=0))/R(H=0)]$\times$100, where H is oriented along
the OOP direction. Above TN, the system is in the paramagnetic phase
characterized by a broad negative MRR (nMRR) due to the field-induced
suppression of spin-flip scattering between conduction electrons and local
magnetic moments. Well below TN at 1.5 K, we observe a negligible MRR up to a
critical field of HC = 8.5 $\pm$ 0.2 T above which, the absolute value of MRR
sharply increases and continues to increase linearly for H$>$HC. The response
of MRR closely follows the measured M vs H traces (Fig. 4B and Fig. S13-S17),
indicating that HC is correlated with the jump in M vs H. As T increases, HC
decreases towards zero at TN, consistent with the magnetization measurements.
These results demonstrate that TaFe1.14Te3 exhibits a relatively strong
coupling between electrical properties and magnetic order. The fact that MRR
decreases as M increases suggests the primary mechanism could be a field-
induced suppression of interlayer spin-flip scattering. However, elucidating
the exact mechanism behind this coupling will require further measurements of
the field-induced magnetic structure.

The coupling between electrical and magnetic properties can also be seen in
the Hall measurements presented in Fig. 4C. In magnetic materials, the Hall
resistance (RHall) is typically determined by two components arising from the
external and internal magnetic fields[35]. In general, RHall is proportional
to the applied H (the slope of which is related to the carrier density) plus
the sample magnetization. These two contributions can be seen clearly seen in
Hall measurements across the magnetic transition (Fig. 4C; see also Fig.
S13-S18). Above TN (at 300 K), since the sample has negligible magnetization
(Fig. S15), the RHall versus H is linear, from which we extract a
corresponding carrier density of 1.30 $\pm$ 0.03 $\times$ 1021 cm–3,
consistent with previous measurements on similar TaFe1+yTe3
stoichiometries[24, 26]. Below TN (130 K), RHall versus H is linear at low H
with the same slope as the 300 K trace, corresponding to the normal Hall
contribution from external H. Once H reaches HC, RHall sharply increases and
then continues to increase linearly with H for H$>$HC. The slope of RHall
versus H when H$>$HC is larger than the slope for H$<$HC due to the additional
Hall component from the linear sample magnetization (Fig. S14). The slope of
RHall versus H for both H$>$HC and H$<$HC has a non-monotonic temperature
dependence which may arise from temperature-dependent magnetic fluctuations
(Fig. S18)[24]. It’s worth emphasizing that other factors could contribute to
RHall, such as temperature- and field-dependent changes in the band structure.
However, our results bear similarities to other TaFe1+yTe3 stoichiometries[24,
26] and ARPES measurements on TaFe1.14Te3 (as will be seen below) show only
minor changes in the band structure across the magnetic transition, indicating
RHall is primarily determined by the sample carrier density and the sample
magnetization (see Fig. S13-S18 for additional data). This clear effect of the
sample magnetization on the measured RHall further demonstrates the strong
coupling between magnetism and electronic properties in TaFe1.14Te3.

Figure 5:  Evolution of the Fermi surface and electronic states of TaFe1.14Te3
across the magnetic transition. ARPES Fermi surface maps at 20 K (A) and 210 K
(B). Dark blue (white) colors correspond to high (low) photoelectron
intensity. The Fermi surfaces are symmetrized at ky = 0 Å-1. In both (A) and
(B), the black dashed rectangle represents the surface Brillouin zone. The
$\bar{\Gamma}\bar{X}$ and $\bar{\Gamma}\bar{Y}$ directions are along (LIP) and
perpendicular (SIP) to the Fe-Te chains, respectively. C) ARPES intensity map
along the $\bar{Y}-\bar{\Gamma}-\bar{Y}$ direction is shown as cut #1 (purple
dashed line in (A)). Calculated non-magnetic band structure is overlayed as
semi-transparent white lines. D) Energy distribution curves (EDCs) at
$\bar{\Gamma}$ and $\bar{Y}$ symmetry points (vertical dashed white lines in
(C)) at 20 K (solid blue lines) and 210 K (solid black lines). E) ARPES
intensity map along the $\bar{X}-\bar{\Gamma}-\bar{X}$ direction is shown as
cut #2 (orange dashed line in (A)). Calculated non-magnetic band structure is
overlayed as semi-transparent white lines. F) EDCs at ky = 0.07 Å-1 () and ky
= 0.65 Å-1 () (vertical dashed white lines in (E)) at 20 K (solid blue lines)
and 210 K (solid black lines). G) ARPES intensity map along cut #3 (magenta
dashed lined in (A)). H) EDCs at kx = 0.30 Å-1 (vertical dashed white line in
(G)) at 20 K and 210 K. All data were acquired with a photon energy of 21.22
eV. For (C), (E), and (G), purple (yellow) colors correspond to low (high)
photoelectron intensity. All calculated band structures were scaled down by
1.4 and shifted down by 0.2 eV.

To experimentally probe the electronic structure of TaFe1.14Te3, we performed
ARPES on a freshly cleaved surface (vdW plane) under ultra-high vacuum (UHV)
across the magnetic transition (Fig. 5). The Fermi surface at 20 and 210 K are
shown in Fig. 5A, B, respectively. Two sets of periodic wave-like Fermi
surfaces (FSs) are identified, indicated by and ’ in Fig. 5A. The modulated
FSs perpendicular to Fe1-Te chain directions (i.e., $\bar{\Gamma}\bar{Y}$)
point to significant inter-chain interactions. The FS features look similar
between the paramagnetic and antiferromagnetic phases, except for the thermal
broadening, consistent with the previous report[27]. The broadened
spectroscopic features are likely a result of the disorder associated with the
Fe2 site.

The ARPES intensity maps along the $\bar{Y}-\bar{\Gamma}-\bar{Y}$ and
$\bar{X}-\bar{\Gamma}-\bar{X}$ paths in the low-T antiferromagnetic phase are
shown in Fig. 5C, E (cut #1 and #2 in Fig. 5A). ARPES intensity maps are
compared to our DFT band structures of non-magnetic TaFeTe3, where the EF was
empirically shifted to best match the ARPES data (additional orbital-resolved
band structures and partial density of states can be found in Fig. S20,S21).
Along the $\bar{X}-\bar{\Gamma}-\bar{X}$ path, we observe two hole-like bands,
and ’, crossing EF. Another less dispersive band () is also observed near EF.
Overall, experimental ARPES intensity maps show reasonable agreement with our
DFT calculations, when the bandwidth of the latter is reduced by a factor of
1.4 (Fig. 5C, E). The necessity of this rescaling signals relatively strong
electron correlations that are not captured by standard DFT. Fig. 5D displays
the energy distribution curves (EDCs) at $\bar{\Gamma}$ and $\bar{Y}$ points
across the magnetic transition. We observe a distinct change in spectral
intensity and a transfer of spectral weight from high-to-low binding energy,
along with a slight shift in the energy of the bands. A more detailed T
dependence reveals that the most significant changes occur below $\approx$100
K (Fig. S22). The evolution of EDCs across the magnetic transition for the and
bands is shown in Fig. 5F. Below the magnetic transition, the band shows an
enhancement in quasiparticle (QP) spectral weight near EF. However, no such
change was observed for the band. ARPES intensity maps along cut #3 (shown as
a dashed line in Fig. 5A) and EDCs are shown in Fig. 5G, H, respectively. A
strong enhancement of the integrated spectral weight of $\approx$16% is
observed within 0 to –1.25 eV in the antiferromagnetic phase, relative to the
paramagnetic phase. These combined results reflect that the magnetic
transition is driven by the electronic structure reconstruction rather than
Fermi surface nesting.

Our results suggest that the electronic states undergo a band-dependent
reconstruction across the magnetic transition due to the interplay between
orbital and spin degrees of freedom. This behavior is known to occur in other
systems containing local moments and itinerant electrons[36, 37, 38, 39], such
as heavy fermion compounds[40], Fe-based superconductors[41, 42], and other
strongly-correlated transition-metal oxides[43, 44]. The coexistence of
itinerant and local-moment magnetism in TaFe1.14Te3, combined with the fact
that TaFe1.14Te3 can be exfoliated down to atomically thin flakes, provides
new opportunities to study such correlated magnetic systems in the 2D limit.

##  Conclusions

Through a combination of magnetic, electronic, and transport measurements,
supported by first-principles DFT calculations, we resolve the interplay
between the magnetic and electronic properties in the layered vdW magnet
TaFe1.14Te3. We performed high-field magnetometry revealing the full
direction-dependent magnetic properties. Calculations and magnetotransport
measurements confirm the metallic nature of TaFe1.14Te3 and display strong
coupling between electronic transport properties and magnetic order.
Temperature-dependent ARPES measurements show minor band shifts and strong
spectral weight renormalization across the magnetic transition. This, combined
with a low observed saturation moment of 2.05-2.12 µB found in both the high-
field magnetometry measurements and DFT calculations, indicate a complex
interplay between local moment and itinerant magnetism in TaFe1.14Te3.
Finally, we demonstrate the isolation of air-stable few-layer flakes of
TaFe1.14Te3 down to the monolayer limit. Altogether, our results establish
TaFe1.14Te3 as an exciting material for 2D spintronics, manifesting both
robust A-type antiferromagnetism, metallic transport properties, and stability
under ambient conditions. Furthermore, the intersection of local-moment and
itinerant magnetism typically occurs in correlated electronic systems,
offering TaFe1.14Te3 as a promising platform for studying magnetism in 2D
correlated electronic materials.

##  Methods

###  Synthesis of TaFe1.14Te3

Single crystals of TaFe1.14Te3 were grown by chemical vapor transport.
Tantalum, iron, tellurium, and TeCl4 powders were combined in a 1:1.15:3:0.02
mole ratio, pressed into a pellet, and sealed in a fused silica tube (7 mm in
diameter and approximately 40 cm in length) under vacuum. The sealed tube was
loaded into a three-zone furnace and heated to a temperature gradient of 700∘C
to 600∘C over 24 hours, with the pellet placed in the hot zone. After seven
days, needle-like crystals were obtained in the sink end of the tube.

###  Energy Dispersive X-ray Spectroscopy (EDX) and Scanning Electron
Microscopy (SEM)

SEM images were acquired on a Zeiss SIGMA VP scanning electron microscope with
a Bruker XFlash 6$|$30 Detector for EDX measurements. Single TaFe1.14Te3
crystals were washed with hexanes, placed on carbon tape, and the surface was
freshly cleaved with Scotch Magic tape immediately before loading into the
chamber. SEM images were acquired with a beam energy of 5 kV. EDX spectra were
acquired with a beam energy of 18 kV. The EDX collection time was
automatically set by the Bruker ESPRIT 2 software using the “precise”
acquisition setting. Elemental compositions and atomic percentages were
estimated by integrating under the characteristic spectrum peaks for each
element using Bruker ESPRIT 2 software.

###  Vibrating Sample Magnetometry (VSM) up to 9T

Vibrating sample magnetometry was conducted on a Quantum Design PPMS Dynacool
system. TaFe1.14Te3 single crystals were attached to a quartz paddle using GE
varnish (which was cured at room temperature under ambient conditions for 45
minutes) and oriented with long in-plane (LIP), short in-plane (SIP), or out-
of-plane (OOP) direction parallel to the applied magnetic field. The same
crystal was used for all direction-dependent measurements. Variable
temperature magnetic susceptibility and magnetic field-dependent magnetization
curves for each orientation were measured during the same measurement cycle.
Samples were removed using a 1:1 ethanol/toluene solution, dried in air, and
then remounted to the quartz paddle using GE varnish.

###  Vibrating Sample Magnetometry (VSM) up to 35T

The high-field magnetization data were obtained at the National High Magnetic
Field Laboratory (NHMFL) using a conventional Vibrating Sample Magnetometer.
The measurement was performed on a few single crystal samples with a total
mass of 19.6 mg glued on a Torlon (polyamidimide) sample holder with GE7031
varnish. A water-cooled resistive magnet was used to apply magnetic fields up
to 35 T.

###  Scanning Tunneling Microscopy/Spectroscopy (STM/S)

STM and STS measurements were conducted in a home-built STM under ultra-high
vacuum at 7.5 K. The tungsten tunneling tip was electrochemically etched and
calibrated against the Au(111) surface state prior to each sample approach.
Crystals were cleaved in vacuum prior to measurement. Topography was acquired
in constant current mode with a set bias of 400 mV and a set current of 50 pA.

###  Transmission Electron Microscopy (TEM)

TaFe1.14Te3 flakes were isolated through mechanical exfoliation of single
crystals and placed on a TEM grid. TEM images were taken with a Thermofisher
Scientific Talos F200X. The sample was slightly tilted to the desired
orientation and bright-field mode imaging was set by using the Objective
Aperture 100 μm.

###  Electrical Transport Device Fabrication

TaFe1.14Te3 crystals were bonded to a 16-pin DIP socket using low-temperature
non-conducting epoxy (Loctite EA 1C) and the top surface was freshly cleaved.
All contacts to bulk TaFe1.14Te3 were made with Field’s metal using a
microsoldering technique[34, 33]. A micromanipulator and heated sample holder
were placed under an optical microscope. The temperature of the sample holder
was raised to 70∘C to melt the Field’s metal. The tip of the micromanipulator
was lowered into the Field’s metal and slowly drawn out to produce a contact
with a few-micron-wide tip. The contact was then aligned on top of the sample
with the micromanipulator and placed on the sample while heating to 100∘C.
Direct electrical connections from the Field’s metal contact to the dip socket
gold pads were made by hand with silver paint (Dupont 4929N) and 25 µm
diameter aluminum wire-bonding wire.

###  Electrical Transport Measurements

Longitudinal and Hall resistances were measured in a 4-terminal configuration
using a Keithley 6221 as a high-precision current source and a Keithley 2182A
as a DC voltmeter. The two instruments were operated in delta mode to reduce
background noise. A source current of 5 mA was used for all measurements
unless otherwise stated. Due to the morphology of the TaFe1.14Te3 crystals,
current and longitudinal resistance were measured parallel to the long in-
plane direction (LIP) and the Hall voltage was measured along the short in-
plane direction (SIP). Variable temperatures between 1.5 K and 300 K and
magnetic fields between -12 T and 12 T were achieved in an Oxford TeslatronPT
dry 4He cryostat.

###  Exfoliation

Thin flakes of TaFe1.14Te3 were isolated using a two-step exfoliation
procedure. First, single TaFe1.14Te3 crystals were cleaved multiple times with
Nitto REVALPHA thermal release tape[45]. Then, Scotch Magic tape was used to
exfoliate the crystals from the thermal release tape and transfer them onto
commercially available polydimethylsiloxane (PDMS) stamps. Once on the PDMS
stamps, the thickness of exfoliated flakes was inferred from atomic force
microscopy and optical contrast.

###  Atomic Force Microscopy (AFM)

Atomic force microscopy was performed in a Bruker Dimension Icon using
OTESPA-R3 tips in tapping mode. Flake thicknesses were extracted using
Gwyddion to measure the height difference between the substrate and the
desired TaFe1.14Te3 flake.

###  X-ray Photoemission Spectroscopy (XPS)

XPS measurements were performed by a VersaProbe II (Physical Electronics)
equipped with Al K X-rays and dual beam neutralization (10 eV Ar+ ions and
electrons) at 45-degree measuring angle. The pass energies for survey and
individual elements are 117.4 eV and 23.5 eV, respectively.

###  Single crystal X-ray diffraction

Single crystal diffraction measurements were collected on TaFe1.14Te3 crystals
using an Agilent Supernova single-crystal diffractometer. The crystals were
mounted onto a MiTeGen MicroLoops holder with paratone oil. The X-ray source
was a Mo K micro-focus tube energized to 50 kV and 0.8 mA. The collection
temperature was maintained between 300 K and 100 K using an Oxford instruments
nitrogen cryostream. The data collection, integration, and reduction were
performed using the Crysalis Pro software suite. The crystal structure was
solved and refined using ShelXT and ShelXL respectively.

###  Powder X-ray diffraction (PXRD)

Powder diffraction patterns were collected on a Panalytical Aeris
diffractometer with a Cu K X-ray source energized to 40 kV and 15 mA. The
X-ray beam was filtered with a Ni filter. The powder sample of TaFe1.14Te3
(prepared by grinding single crystals in liquid nitrogen) was mounted on a Si-
zero background holder which was spun to reduce preferred orientation.

###  Heat capacity

Heat capacity measurements were performed with a Quantum Design PPMS Dynacool
system. The background heat capacity of the sample puck plus grease (Apiezon N
grease) was measured over the desired temperature and magnetic field ranges
before the sample was loaded onto the platform. The background was then
subtracted from the total measured heat capacity (sample plus grease and puck)
to obtain the heat capacity of the sample.

###  Angle-resolved Photoemission Spectroscopy (ARPES)

The sample was attached to a sample holder using Ag-epoxy and cleaved in-situ
using Kapton tape, just before the ARPES measurements. The ARPES experiments
were carried out at OASIS-laboratory at Brookhaven National Laboratory using a
Scienta SES-R4000 electron spectrometer with monochromatized He-I (21.22 eV)
radiation (VUV-5k)[46]. The total instrumental energy resolution was
$\approx$10 meV. The angular resolution was better than 0.15 and 0.4 along and
perpendicular to the slit of the analyzer, respectively.

###  Preparation of TaFe1.14Te3 powder samples for magnetometry measurements
under pressure

Single crystals of TaFe1.14Te3 were placed in a thin porcelain crucible with
enough liquid N2 to fully submerge the crystals. The crystals were then ground
with a thermally equilibrated pestle for 5 mins. The resulting powder was
rinsed with acetone to remove residual moisture from condensation.

###  Determination of applied hydrostatic pressure for magnetometry
measurements under pressure

Since the superconducting (SC) critical temperature (TC) of Pb is well-known
to linearly depend upon applied hydrostatic pressure (P) at a rate of dTC/dP =
0.379 K$\cdot$GPa-1[47], we use the measured TC of Pb to determine the P on
TaFe1.14Te3. First, the Pb plus TaFe1.14Te3 sample is zero-field cooled below
the SC transition to 6 K. Then, the magnetic susceptibility () versus
temperature (T) is measured with a small measuring field of 5 Oe (much smaller
than the zero-temperature upper critical field of Pb[48]). versus T is
measured at a rate of 0.05 K$\cdot$min-1 to ensure the transition is precisely
resolved and traces with increasing and decreasing T were measured. The Pb TC
is extracted by finding the condition where = 0.5N (N is the susceptibility in
the normal state).

###  Vibrating sample magnetometry under hydrostatic pressure

All vibrating sample magnetometry under P was conducted on a Quantum Design
PPMS Dynacool system using the commercially-available HMD high-pressure cell.
Before and after the VSM measurements, PXRD was used to confirm there was no
significant change in structure upon grinding or after applying maximum
pressure (Fig. S9). The powder was then combined with Daphne 7373 oil and a
$\approx$1-2 mm long wire of Pb in a Teflon capsule, which was then inserted
into the pressure cell. The variable temperature scans and field-dependent
magnetic susceptibility curves for each P were measured during the same
measurement cycle. The measurements performed at different pressures were done
sequentially with increasing pressure (from zero applied pressure up to the
maximum achievable pressure). After the final maximum pressure measurement,
the capsule containing the TaFe1.14Te3 powder, Daphne 7373 oil, and the Pb
manometer was removed, fixed to a brass paddle with GE varnish, and re-
measured as a consistency check of the zero-pressure measurement.

###  Computational Methods

The computational results were obtained using density functional theory, as
implemented in the QUANTUM ESPRESSO package[49, 50]. We used projector-
augmented wave pseudopotentials (Ta.pbe-spn-kjpaw_psl.1.0.0.UPF, Fe.pbe-spn-
kjpaw_psl.1.0.0.UPF, and Te.pbe-n-kjpaw_psl.1.0.0.UPF from http://www.quantum-
espresso.org) with the Perdew-Burke-Ernzerhof exchange-correlation
functional[51], with nonlinear core correction and scalar relativistic
effects. Gaussian smearing was set to 0.005 Ry. The wave function and density
energy cutoffs were 100 Ry and 400 Ry, respectively. The Brillouin zone was
sampled with a 7x7x7 k-space mesh for the paramagnetic, primitive cells and
with a 3x7x7 k-space mesh for the 2x1x1 AFM supercells. The unit cell was
taken from MaterialsProject (mp-8848)[52]. Relaxed positions of atoms within
the unit cell were used.

##  Acknowledgements

We would like to thank Daniel Chica and Amymarie Bartholomew for their help in
analyzing SCXRD data and Mike Ziebel for useful discussions on magnetic data.
We would also like to acknowledge the use of Python-based data acquisition
software developed by Maëlle Kapfer for all transport measurements. Synthesis
and structural/compositional characterization of layered metallic
antiferromagnets was supported by the National Science Foundation (NSF)
through the Columbia University Materials Research Science and Engineering
Center (MRSEC) on Precision-Assembled Quantum Materials DMR-2011738.
Magnetotransport measurements were supported as part of Programmable Quantum
Materials, an Energy Frontier Research Center funded by the U.S. Department of
Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award DE-
SC0019443. Magnetic characterization was supported by the Air Force Office of
Scientific Research award FA9550-22-1-0389. Imaging experiments were supported
by the NSF CAREER award DMR-1751949. S.J.B. acknowledges support from the NSF
Award DGE-2036197. The authors acknowledge the use of facilities and
instrumentation supported by the NSF through Columbia University, Columbia
Nano Initiative, and the Materials Research Science and Engineering Center
DMR-2011738. The National High Magnetic Field Laboratory is supported by the
NSF through NSF/DMR-1644779 and the State of Florida. The research at
Brookhaven National Laboratory was supported by the US Department of Energy,
Office of Basic Energy Sciences, Contract No. DESC0012704.

##  Author Contributions

S.Y.H. and E.J.T. collected and analyzed the SCXRD data. S.Y.H. and R.W.
optimized the synthesis procedure and synthesized the single crystals. S.Y.H.
and E.J.T. performed the SEM/EDX and analyzed the data. S.T. performed the STM
and STS experiments. A.Z. collected and analyzed the TEM data. S.J.B.
performed DFT calculations. S.Y.H. and E.J.T. performed the low-field
magnetometry. S.Y.H., E.J.T., and E-S.C. performed the high-magnetometry.
S.Y.H. prepared the single-crystal transport devices and E.J.T. performed the
transport measurements and analyzed the data. A.K. collected and analyzed the
ARPES data. T-D.L. performed the XPS experiments. S.Y.H. and E.J.T. exfoliated
few-layer flakes and performed the atomic force microscopy and contrast
analysis. S.Y.H. and E.J.T. performed heat capacity measurements and analyzed
the data. S.Y.H. performed and analyzed the PXRD data. The manuscript was
prepared with input from all co-authors.

##  Supporting Information

Supporting information is available at the end of this document after the
references.

##  Conflict of Interest

The authors declare no conflict of interest.

## References

  * Ahn [2020] E. C. Ahn, 2d materials for spintronic devices, npj 2D Materials and Applications 4, 17 (2020).
  * Arora [2021] A. Arora, Magneto-optics of layered two-dimensional semiconductors and heterostructures: Progress and prospects, Journal of Applied Physics 129, 120902 (2021).
  * Hendriks and Guimarães [2021] F. Hendriks and M. H. D. Guimarães, Enhancing magneto-optic effects in two-dimensional magnets by thin-film interference, AIP Advances 11, 035132 (2021).
  * Zhang  _et al._ [2021a] Y. Zhang, H. Xu, J. Feng, H. Wu, G. Yu, and X. Han, Magnetic two-dimensional van der waals materials for spintronic devices, Chinese Physics B 30, 118504 (2021a).
  * Lan  _et al._ [2020] T. Lan, B. Ding, and B. Liu, Magneto-optic effect of two-dimensional materials and related applications, Nano Select 1, 298 (2020).
  * Chen  _et al._ [2004] Z. Chen, B. Wang, D. Y. Xing, and J. Wang, A spin injector, Applied Physics Letters 85, 2553 (2004).
  * Ningrum  _et al._ [2020] V. P. Ningrum, B. Liu, W. Wang, Y. Yin, Y. Cao, C. Zha, H. Xie, X. Jiang, Y. Sun, S. Qin, X. Chen, T. Qin, C. Zhu, L. Wang, and W. Huang, Recent advances in two-dimensional magnets: Physics and devices towards spintronic applications, Research 2020 (2020).
  * Wang  _et al._ [2022] Q. H. Wang, A. Bedoya-Pinto, M. Blei, A. H. Dismukes, A. Hamo, S. Jenkins, M. Koperski, Y. Liu, Q.-C. Sun, E. J. Telford, H. H. Kim, M. Augustin, U. Vool, J.-X. Yin, L. H. Li, A. Falin, C. R. Dean, F. Casanova, R. F. L. Evans, M. Chshiev, A. Mishchenko, C. Petrovic, R. He, L. Zhao, A. W. Tsen, B. D. Gerardot, M. Brotons-Gisbert, Z. Guguchia, X. Roy, S. Tongay, Z. Wang, M. Z. Hasan, J. Wrachtrup, A. Yacoby, A. Fert, S. Parkin, K. S. Novoselov, P. Dai, L. Balicas, and E. J. G. Santos, The magnetic genome of two-dimensional van der waals materials, ACS Nano 16, 6960 (2022).
  * Shin  _et al._ [2022] I. Shin, W. J. Cho, E.-S. An, S. Park, H.-W. Jeong, S. Jang, W. J. Baek, S. Y. Park, D.-H. Yang, J. H. Seo, G.-Y. Kim, M. N. Ali, S.-Y. Choi, H.-W. Lee, J. S. Kim, S. D. Kim, and G.-H. Lee, Spin–orbit torque switching in an all-van der waals heterostructure, Advanced Materials 34, 2101730 (2022).
  * Martin  _et al._ [2023] F. Martin, K. Lee, M. Schmitt, A. Liedtke, A. Shahee, H. T. Simensen, T. Scholz, T. G. Saunderson, D. Go, M. Gradhand, Y. Mokrousov, T. Denneulin, A. Kovács, B. Lotsch, A. Brataas, and M. Kläui, Strong bulk spin–orbit torques quantified in the van der waals ferromagnet Fe3GeTe2, Materials Research Letters 11, 84 (2023).
  * Jungwirth  _et al._ [2016] T. Jungwirth, X. Marti, P. Wadley, and J. Wunderlich, Antiferromagnetic spintronics, Nature Nanotechnology 11, 231 (2016).
  * Rezende  _et al._ [2019] S. M. Rezende, A. Azevedo, and R. L. Rodríguez-Suárez, Introduction to antiferromagnetic magnons, Journal of Applied Physics 126, 151101 (2019).
  * Yan  _et al._ [2020] H. Yan, Z. Feng, P. Qin, X. Zhou, H. Guo, X. Wang, H. Chen, X. Zhang, H. Wu, C. Jiang, and Z. Liu, Electric-field-controlled antiferromagnetic spintronic devices, Advanced Materials 32, 1905603 (2020).
  * Ueda [1977] K. Ueda, Electrical resistivity of antiferromagnetic metals, Journal of the Physical Society of Japan 43, 1497 (1977).
  * Zhang  _et al._ [2021b] X.-X. Zhang, S. Jiang, J. Lee, C. Lee, K. F. Mak, and J. Shan, Spin dynamics slowdown near the antiferromagnetic critical point in atomically thin FePS3, Nano Letters 21, 5045 (2021b).
  * Bai  _et al._ [2020] H. Bai, X. Zhou, Y. Zhou, X. Chen, Y. You, F. Pan, and C. Song, Functional antiferromagnets for potential applications on high-density storage and high frequency, Journal of Applied Physics 128, 210901 (2020).
  * Rahman  _et al._ [2021] S. Rahman, J. F. Torres, A. R. Khan, and Y. Lu, Recent developments in van der waals antiferromagnetic 2d materials: Synthesis, characterization, and device implementation, ACS Nano 15, 17175 (2021).
  * Mak  _et al._ [2019] K. F. Mak, J. Shan, and D. C. Ralph, Probing and controlling magnetic states in 2d layered magnetic materials, Nature Reviews Physics 1, 646 (2019).
  * Neuhausen  _et al._ [1993] J. Neuhausen, E. Potthoff, W. Tremel, J. Ensling, P. Gütlich, and R. K. Kremer, TaFe1.14Te3, a new low-dimensional ternary tantalum telluride., ChemInform 24 (1993).
  * Pérez Vicente  _et al._ [1998] C. Pérez Vicente, M. Womes, J. C. Jumas, L. Sánchez, and J. L. Tirado, Distribution of cations and vacancies in TaFe1.25Te3 studied by mössbauer spectroscopy, The Journal of Physical Chemistry B 102, 8712 (1998).
  * Badding  _et al._ [1992] M. E. Badding, J. Li, F. J. DiSalvo, W. Zhou, and P. P. Edwards, Characterization of TaFe1.25Te3, a new layered telluride with an unusual metal network structure, Journal of Solid State Chemistry 100, 313 (1992).
  * Opačić  _et al._ [2017] M. Opačić, N. Lazarević, D. Tanasković, M. M. Radonjić, A. Milosavljević, Y. Ma, C. Petrovic, and Z. V. Popović, Small influence of magnetic ordering on lattice dynamics in TeFe1.25Te3, Physical Review B 96, 174303 (2017).
  * Ke  _et al._ [2012] X. Ke, B. Qian, H. Cao, J. Hu, G. C. Wang, and Z. Q. Mao, Magnetic structure of quasi-one-dimensional antiferromagnetic TaFe1+yTe3, Physical Review B 85, 214404 (2012).
  * Liu  _et al._ [2011] R. H. Liu, M. Zhang, P. Cheng, Y. J. Yan, Z. J. Xiang, J. J. Ying, X. F. Wang, A. F. Wang, G. J. Ye, X. G. Luo, and X. H. Chen, Spin-density-wave transition of Fe1 zigzag chains and metamagnetic transition of Fe2 in TaFe1+yTe3, Physical Review B 84, 184432 (2011).
  * Liu  _et al._ [2021] Y. Liu, J. J. Bao, C. Q. Xu, W. H. Jiao, H. Zhang, L. C. Xu, Z. Zhu, H. Y. Yang, Y. Zhou, Z. Ren, P. K. Biswas, S. K. Ghosh, Z. Yang, X. Ke, G. H. Cao, and X. Xu, Coupling between antiferromagnetic and spin-glass orders in the quasi-one-dimensional iron telluride TaFe1+xTe3 (x=0.25), Physical Review B 104, 104418 (2021).
  * Roy Chowdhury  _et al._ [2022] R. Roy Chowdhury, S. DuttaGupta, C. Patra, A. Kataria, S. Fukami, and R. P. Singh, Anisotropic magnetotransport in the layered antiferromagnet TaFe1.25Te3, Physical Review Materials 6, 084408 (2022).
  * Xu  _et al._ [2015] M. Xu, L.-M. Wang, R. Peng, Q.-Q. Ge, F. Chen, Z.-R. Ye, Y. Zhang, S.-D. Chen, M. Xia, R.-H. Liu, M. Shi, X.-H. Chen, W.-G. Yin, W. Ku, B.-P. Xie, D.-L. Feng, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, M. Matsunami, and S. Kimura, Electronic structure reconstruction across the antiferromagnetic transition in TaFe1.23Te3 spin ladder, Chinese Physics Letters 32, 027401 (2015).
  * Aruga  _et al._ [1988] H. Aruga, A. Ito, H. Wakabayashi, and T. Goto, Field-dependent phenomena in reentrant-spin-glass: Fe(x)mn(1-x)tio(3) with x=0.60, 0.65, and 0.75, Journal of the Physical Society of Japan 57, 2636 (1988).
  * Ito  _et al._ [1990] A. Ito, S. Morimoto, and H. Aruga, Studies on spin-glass freezing and antiferromagnetic long-range order in an ising spin-glass system fe(x)mn(1-x)tio(3), Hyperfine Interactions 54, 567 (1990).
  * Katori and Ito [1993] H. A. Katori and A. Ito, Magnetic property and phase diagram of a frustrated system with competing exchange interactions, fe(x)mn(1-x)tio(3)., Journal of the Physical Society of Japan 62, 4488 (1993).
  * Yoshizawa  _et al._ [1989] H. Yoshizawa, S. Mitsuda, H. Aruga, and A. Ito, Reentrant spin-glass transition and a mixed phase in an ising system fe(x)mn(1-x)tio(3), Journal of the Physical Society of Japan 58, 1416 (1989).
  * Yamashita and Hayes [2008] T. Yamashita and P. Hayes, Analysis of xps spectra of Fe2+ and Fe3+ ions in oxide materials, Applied Surface Science 254, 2441 (2008).
  * Girit and Zettl [2007] Ç. Ŏ. Girit and A. Zettl, Soldering to a single atomic layer, Applied Physics Letters 91 (2007).
  * Kerelsky  _et al._ [2019] A. Kerelsky, L. J. McGilly, D. M. Kennes, L. Xian, M. Yankowitz, S. Chen, K. Watanabe, T. Taniguchi, J. Hone, C. Dean, A. Rubio, and A. N. Pasupathy, Maximized electron interactions at the magic angle in twisted bilayer graphene, Nature 572, 95 (2019).
  * Pugh and Rostoker [1953] E. M. Pugh and N. Rostoker, Hall effect in ferromagnetic metals, Reviews of Modern Physics 25, 151 (1953).
  * Zhang  _et al._ [2010] Y. Zhang, F. Chen, C. He, L. X. Yang, B. P. Xie, Y. L. Xie, X. H. Chen, M. Fang, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, J. P. Hu, and D. L. Feng, Strong correlations and spin-density-wave phase induced by a massive spectral weight redistribution in -Fe1.06Te, Physical Review B 82, 165113 (2010).
  * Xu  _et al._ [2020] X. Xu, Y. W. Li, S. R. Duan, S. L. Zhang, Y. J. Chen, L. Kang, A. J. Liang, C. Chen, W. Xia, Y. Xu, P. Malinowski, X. D. Xu, J. H. Chu, G. Li, Y. F. Guo, Z. K. Liu, L. X. Yang, and Y. L. Chen, Signature for non-stoner ferromagnetism in the van der waals ferromagnet Fe3GeTe2, Physical Review B 101, 201104 (2020).
  * Schmitt  _et al._ [2012] S. Schmitt, N. Grewe, and T. Jabben, Itinerant and local-moment magnetism in strongly correlated electron systems, Physical Review B 85, 024404 (2012).
  * Liu  _et al._ [2013] Z. K. Liu, R. H. He, D. H. Lu, M. Yi, Y. L. Chen, M. Hashimoto, R. G. Moore, S. K. Mo, E. A. Nowadnick, J. Hu, T. J. Liu, Z. Q. Mao, T. P. Devereaux, Z. Hussain, and Z. X. Shen, Measurement of coherent polarons in the strongly coupled antiferromagnetically ordered iron-chalcogenide Fe1.02Te using angle-resolved photoemission spectroscopy, Physical Review Letters 110, 037003 (2013).
  * Chen  _et al._ [2019] Q. Y. Chen, X. B. Luo, D. H. Xie, M. L. Li, X. Y. Ji, R. Zhou, Y. B. Huang, W. Zhang, W. Feng, Y. Zhang, L. Huang, Q. Q. Hao, Q. Liu, X. G. Zhu, Y. Liu, P. Zhang, X. C. Lai, Q. Si, and S. Y. Tan, Orbital-selective kondo entanglement and antiferromagnetic order in USb2, Phys. Rev. Lett. 123, 106402 (2019).
  * Zhang  _et al._ [2012] Y. Zhang, C. He, Z. R. Ye, J. Jiang, F. Chen, M. Xu, Q. Q. Ge, B. P. Xie, J. Wei, M. Aeschlimann, X. Y. Cui, M. Shi, J. P. Hu, and D. L. Feng, Symmetry breaking via orbital-dependent reconstruction of electronic structure in detwinned nafeas, Physical Review B 85, 085121 (2012).
  * Yang  _et al._ [2009] L. X. Yang, Y. Zhang, H. W. Ou, J. F. Zhao, D. W. Shen, B. Zhou, J. Wei, F. Chen, M. Xu, C. He, Y. Chen, Z. D. Wang, X. F. Wang, T. Wu, G. Wu, X. H. Chen, M. Arita, K. Shimada, M. Taniguchi, Z. Y. Lu, T. Xiang, and D. L. Feng, Electronic structure and unusual exchange splitting in the spin-density-wave state of the BaFe2As2 parent compound of iron-based superconductors, Physical Review Letters 102, 107002 (2009).
  * Kundu  _et al._ [2021] A. K. Kundu, S. Barman, and K. S. R. Menon, Role of surface termination in the metal–insulator transition of V2O3(0001) ultrathin films, ACS Applied Materials & Interfaces 13, 20779 (2021).
  * Meinders  _et al._ [1993] M. B. J. Meinders, H. Eskes, and G. A. Sawatzky, Spectral-weight transfer: Breakdown of low-energy-scale sum rules in correlated systems, Physical Review B 48, 3916 (1993).
  * Deng  _et al._ [2018] Y. Deng, Y. Yu, Y. Song, J. Zhang, N. Z. Wang, Z. Sun, Y. Yi, Y. Z. Wu, S. Wu, J. Zhu, J. Wang, X. H. Chen, and Y. Zhang, Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2, Nature 563, 94 (2018).
  * Kim  _et al._ [2022] C. K. Kim, I. K. Drozdov, K. Fujita, J. C. S. Davis, I. Božović, and T. Valla, In-situ angle-resolved photoemission spectroscopy of copper-oxide thin films synthesized by molecular beam epitaxy, Journal of Electron Spectroscopy and Related Phenomena 257, 146775 (2022).
  * RNS [2016] High pressure cell user manual (2016).
  * Chanin and Torre [1972] G. Chanin and J. P. Torre, Critical-field curve of superconducting lead, Physical Review B 5, 4357 (1972).
  * Giannozzi  _et al._ [2009] P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G. L. Chiarotti, M. Cococcioni, I. Dabo, A. D. Corso, S. de Gironcoli, S. Fabris, G. Fratesi, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A. P. Seitsonen, A. Smogunov, P. Umari, and R. M. Wentzcovitch, Quantum espresso: a modular and open-source software project for quantum simulations of materials, Journal of Physics: Condensed Matter 21, 395502 (2009).
  * Giannozzi  _et al._ [2017] P. Giannozzi, O. Andreussi, T. Brumme, O. Bunau, M. B. Nardelli, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, M. Cococcioni, N. Colonna, I. Carnimeo, A. D. Corso, S. de Gironcoli, P. Delugas, R. A. DiStasio, A. Ferretti, A. Floris, G. Fratesi, G. Fugallo, R. Gebauer, U. Gerstmann, F. Giustino, T. Gorni, J. Jia, M. Kawamura, H.-Y. Ko, A. Kokalj, E. Küçükbenli, M. Lazzeri, M. Marsili, N. Marzari, F. Mauri, N. L. Nguyen, H.-V. Nguyen, A. O. de-la Roza, L. Paulatto, S. Poncé, D. Rocca, R. Sabatini, B. Santra, M. Schlipf, A. P. Seitsonen, A. Smogunov, I. Timrov, T. Thonhauser, P. Umari, N. Vast, X. Wu, and S. Baroni, Advanced capabilities for materials modelling with quantum espresso, Journal of Physics: Condensed Matter 29, 465901 (2017).
  * Perdew  _et al._ [1996] J. P. Perdew, K. Burke, and M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77, 3865 (1996).
  * Jain  _et al._ [2013] A. Jain, S. P. Ong, G. Hautier, W. Chen, W. D. Richards, S. Dacek, S. Cholia, D. Gunter, D. Skinner, G. Ceder, and K. A. Persson, Commentary: The Materials Project: A materials genome approach to accelerating materials innovation, APL Materials 1 (2013).

##  Supporting Information

###### List of Figures

  1. 1 Structure and composition of TaFe1.14Te3
  2. 2 Atomic-scale characterization of TaFe1.14Te3
  3. 3 High-field magnetic properties of TaFe1.14Te3
  4. 4 Electronic transport properties of TaFe1.14Te3
  5. 5 Evolution of the Fermi surface and electronic states of TaFe1.14Te3 across the magnetic transition.
  6. S1 Mechanical exfoliation of TaFe1.14Te3 flakes
  7. S2 Scanning tunneling microscopy and spectroscopy of TaFe1.14Te3
  8. S3 Field-dependent magnetic susceptibility on TaFe1.14Te3
  9. S4 Temperature-dependent magnetization for TaFe1.14Te3
  10. S5 Specific heat capacity of TaFe1.14Te3
  11. S6 Observation of the spin-glass phase in TaFe1.14Te3
  12. S7 Powderization enhancement of the spin-glass phase in TaFe1.14Te3
  13. S8 Magnetic properties of TaFe1.14Te3 spin-glass phase under hydrostatic pressure
  14. S9 Powder X-ray diffraction of bulk TaFe1.14Te3 crystals before and after grinding
  15. S10 Analysis of TaFe1.14Te3 high-field magnetometry at 1.5 K
  16. S11 High-field magnetometry on two TaFe1.14Te3 single crystals
  17. S12 Background high-field magnetization from the sample paddle
  18. S13 Analysis of the metamagnetic transition far below TN in TaFe1.14Te3
  19. S14 Analysis of the metamagnetic transition near TN in TaFe1.14Te3
  20. S15 Analysis of magnetometry and transport above TN in TaFe1.14Te3
  21. S16 Temperature dependence of the first metamagnetic transition field in TaFe1.14Te3
  22. S17 Temperature dependence of the 12 T MRR and Hall resistance in TaFe1.14Te3
  23. S18 Temperature dependence of anti-symmetrized Hall data in TaFe1.14Te3
  24. S19 Current dependence of magnetotransport in TaFe1.14Te3
  25. S20  Calculated band structures for TaFeTe3 and TaFe2Te3
  26. S21 Element-resolved calculated partial density of states (PDOS) for TaFe1+yTe3
  27. S22 Temperature dependence of ARPES spectra
  28. S23 X-ray photoelectron spectroscopy on bulk TaFe1.14Te3

###### List of Tables

  1. S1 Crystallographic parameters determined through SCXRD for TaFe1.14Te3 at various temperatures
  2. S2 Extracted chemical compositions for multiple TaFe1.14Te3 growth batches
  3. S3 Calculated Löwdin charge and magnetic moments for TaFe1+yTe3

Figure S1:  Mechanical exfoliation of TaFe1.14Te3 flakes. A, E) Grey-scale optical images of two sample TaFe1.14Te3 flakes exfoliated onto PDMS using the previously-described tape method. White and black colors correspond to the PDMS substrate and thick TaFe1.14Te3 flakes, respectively. In (A), the extracted optical contrast for 1, 3, and 4L regions is denoted. B-D) tapping-mode atomic force microscope topography (B), amplitude error (C), and phase (D) for the region in (A) defined by the dashed black box. The inset of (B) shows a height-profile line cut of the step edge. F-H) tapping-mode atomic force microscope topography (F), amplitude error (G), and phase (H) for the region in (E) defined by the dashed black box. Figure S2:  Scanning tunneling microscopy and spectroscopy of TaFe1.14Te3. A) Scanning tunneling microscopy image of bulk TaFe1.14Te3 along the out-of-plane direction at T = 7.5 K. The image was obtained in constant current mode (Vb = 400 mV, I = 50 pA). B) Local density of states (LDOS) versus energy at 7.5 K and zero magnetic field. The trace is a line-average scan across multiple TaFe1.14Te3 chains. The direction and length of the line-scan average are denoted by a black dashed line in (A). C) Zoom-in of the line-averaged LDOS versus energy trace at 7.5 K and zero magnetic field. Figure S3:  Field-dependent magnetic susceptibility on TaFe1.14Te3. A-C) Field-cooled magnetic susceptibility versus temperature for magnetic fields oriented along the out-of-plane (A), long in-plane (B), and short-in-plane (C) directions. The magnetic field at which each trace was taken is given in the insets. TN is denoted by a dashed black line in each plot. Figure S4:  Temperature-dependent magnetization data TaFe1.14Te3. A-C) Color maps of magnetization versus magnetic field (x-axis) and temperature (y-axis) for magnetic fields oriented along the out-of-plane (A), long in-plane (B), and short-in-plane (C) directions. The color bar scale is given above each plot. TN is denoted by a dashed black line in each plot. Figure S5:  Specific heat capacity of TaFe1.14Te3. A) Specific heat capacity versus temperature at zero magnetic field. B) Plot of specific heat capacity divided by the temperature versus the temperature squared. The dashed black line is a linear fit to the data. The fit equation and extracted fit parameters are given in the inset. C) Specific heat capacity versus temperature across the PM-AFM transition at zero magnetic field (solid black dots) and 9 T (solid red dots). The Néel temperature at 0 T and 9 T is denoted by a black and red dashed line, respectively. Figure S6:  Observation of the spin-glass phase in TaFe1.14Te3. A-C) Magnetic susceptibility versus temperature for magnetic fields oriented along the out-of-plane (A), long in-plane (B), and short-in-plane (C) directions. Both field-cooled and zero-field-cooled traces are shown. All traces were acquired with a magnetic field of 25 mT. TN is denoted by a dashed black line in each plot. Figure S7:  Powderization enhancement of the spin-glass phase in TaFe1.14Te3. A-D) Magnetic susceptibility versus temperature with a measuring field of 0.01 T (A), 0.1 T (B), 1 T (C), and 9 T (D). Both field-cooled and zero-field-cooled traces are shown and denoted. Top panels are collected from a single TaFe1.14Te3 crystal with the magnetic field applied parallel to the short in-plane direction. Bottom panels are collected from the same powderized crystal. Figure S8:  Magnetic properties of TaFe1.14Te3 spin-glass phase under hydrostatic pressure. A) Magnetic susceptibility versus temperature across the superconducting transition for the lead manometer for various applied pressures. The corresponding applied pressure is given in the inset. All traces were offset and normalized for clarity. A measuring field of 5 Oe was used. B) Field-cooled (dashed traces) and zero-field-cooled (solid traces) magnetic susceptibility versus temperature for various applied pressures. The corresponding pressure is given in the inset. A measuring field of 1000 Oe was used. C) Magnetization versus magnetic field at 2 K for various applied pressures. Due to the pressure-cell preparation, the magnetic field direction is averaged along all crystal axes. The corresponding pressure is given in the inset. For all panels, measurements were performed in order of increasing pressure. The final measurement (0.000 GPa) is a reference measurement of the sample plus Teflon capsule measured outside of the pressure cell on a brass paddle sample mount.  Figure S9:  Powder X-ray diffraction of bulk TaFe1.14Te3 crystals before and after grinding. Powder X-ray diffraction (PXRD) intensity versus 2 for the empty puck (solid black line), a single crystal of TaFe1.14Te3 (solid red line), a TaFe1.14Te3 single crystal ground with LN2 (solid blue line), and a TaFe1.14Te3 single crystal ground with LN2 after being pressurized up to 1.3 GPa (solid green line). Simulated TaFe1.14Te3 PXRD peaks are denoted with black tick marks. Figure S10:  Analysis of TaFe1.14Te3 high-field magnetometry at 1.5 K. A-C) Magnetization (solid blue lines) and derivative of magnetization (solid yellow lines) versus magnetic field at 1.5 K for magnetic fields oriented along the out-of-plane (A), long in-plane (B), and short in-plane (C) directions. In each plot, the extracted saturation magnetization and saturation magnetic field are given in the inset. Figure S11:  High-field magnetometry on two TaFe1.14Te3 single crystals. A-C) Magnetization versus magnetic field at 1.5 K for magnetic fields oriented along the out-of-plane (A), long in-plane (B), and short in-plane (C) directions for two separate TaFe1.14Te3 crystals. Each plot’s blue and red traces correspond to the different TaFe1.14Te3 crystals. In each plot, the extracted saturation magnetization is given in the inset. Figure S12:  Background high-field magnetization from the sample paddle. Magnetization versus magnetic field at 1.5 K for two sample paddles with GE varnish. The blue and red traces correspond to the different paddles. Figure S13:  Analysis of the metamagnetic transition far below TN in TaFe1.14Te3. A) Magnetization (solid black line) and the derivative of magnetization (solid red line) versus magnetic field at 1.5 K for fields parallel to the out-of-plane direction. B) Magnetoresistance ratio, MRR = [R(H)-R(H=0)]/R(H=0)$\times$100, versus magnetic field at 1.5 K for fields parallel to the out-of-plane direction. The inset is an optical image of the device along with the measurement configuration. C) Hall resistance versus magnetic field at 1.5 K. Two distinct linear regions (denoted by dashed black lines) are observed below TN. The inset is an optical image of the device along with the measurement configuration. In A-C, the vertical gray bars demarcate the magnetic field at which a spin-flop metamagnetic transition occurs (HC). This spin-flop transition (A) results in a sharp decrease in MRR (B) and a sharp increase in the anomalous Hall contribution to RHall (C). Figure S14:  Analysis of the metamagnetic transition near TN in TaFe1.14Te3. A) Magnetization (solid black line) and the derivative of magnetization (solid red line) versus magnetic field at 130 K for fields parallel to the out-of-plane direction. B) Magnetoresistance ratio, MRR = [R(H)-R(H=0)]/R(H=0)$\times$100, versus magnetic field at 130 K for fields parallel to the out-of-plane direction. The inset is an optical image of the device along with the measurement configuration. C) Hall resistance versus magnetic field at 130 K. Two distinct linear regions (denoted by dashed black lines) are observed below TN. The inset is an optical image of the device along with the measurement configuration. In A-C, the vertical gray bars demarcate the magnetic field at which a spin-flop metamagnetic transition occurs (HC). This spin-flop transition (A) results in a sharp decrease in MRR (B) and a sharp increase in the anomalous Hall contribution to RHall (C). Figure S15:  Analysis of magnetometry and transport above TN in TaFe1.14Te3. A) Magnetization (solid black line) versus magnetic field at 300 K for fields parallel to the out-of-plane direction. B) Magnetoresistance ratio, MRR = [R(H)-R(H=0)]/R(H=0)$\times$100, versus magnetic field at 300 K for fields parallel to the out-of-plane direction. The inset is an optical image of the device along with the measurement configuration. C) Hall resistance versus magnetic field at 300 K. A single linear region (denoted by a dashed black line) is observed over the entire field range. The inset is an optical image of the device along with the measurement configuration. Figure S16:  Temperature dependence of the first metamagnetic transition field in TaFe1.14Te3. The magnetic field at which the first metamagnetic transition occurs as measured by magnetometry (solid black pluses and red crosses), longitudinal magnetoresistance (solid blue circles), and Hall resistance (solid green diamonds). The dashed black line is a guide to the eye. The Néel temperature is denoted by a solid gray line. The magnetic field was aligned parallel to the out-of-plane axis for all measurements. Figure S17:  Temperature dependence of the 12 T MRR and Hall resistance in TaFe1.14Te3. Left axis: MRR at 12 T versus temperature extracted from longitudinal resistance measurements (solid blue diamonds) and the symmetric component of the Hall resistance measurements (solid blue circles). Right axis: Hall resistance at 12 T versus temperature. The Hall resistance was anti-symmetrized to remove components of the raw data that were symmetric in the magnetic field. The Néel temperature is denoted by a solid gray line. The magnetic field was oriented parallel to the out-of-plane axis for all measurements. Figure S18:  Temperature dependence of anti-symmetrized Hall data in TaFe1.14Te3. Anti-symmetrized Hall resistance versus magnetic field at various temperatures for fields parallel to the out-of-plane direction. Both forward and backward traces are shown. The temperature at which each trace was taken is given in the inset. The dashed black lines denote the zero crossings. The inset is an optical image of the device along with the measurement configuration. Figure S19:  Current dependence of magnetotransport in TaFe1.14Te3. Magnetoresistance ratio, MRR = [R(H)-R(H=0)]/R(H=0)$\times$100, versus magnetic field at various source currents for fields parallel to the out-of-plane direction. Both forward and backward traces are shown. The traces were all taken at 1.5 K. The dashed black lines denote the zero crossings. The inset is an optical image of the device along with the measurement configuration. Figure S20:  Calculated band structures for TaFeTe3 and TaFe2Te3. A, B) Element-resolved band structure calculations for TaFeTe3 in the antiferromagnetic (A) and non-magnetic (B) configurations. Red squares, blue circles, and green triangles correspond to Fe 3d orbitals, Ta 5d orbitals, and Te 5p orbitals. C, D). Element-resolved band structure calculations for TaFe2Te3 in the antiferromagnetic (C) and non-magnetic (D) state. Red squares, blue circles, and green triangles correspond to Fe 3d orbitals, Ta 5d orbitals, and Te 5p orbitals. Figure S21:  Element-resolved calculated partial density of states (PDOS) for TaFe1+yTe3. A, B) Element-resolved partial density of states (PDOS) calculated for TaFeTe3 in the non-magnetic (A) and antiferromagnetic (B) configuration. C, D) Element-resolved partial density of states (PDOS) calculated for TaFe2Te3 in the non-magnetic (C) and antiferromagnetic (D) configuration.  Figure S22:  Temperature dependence of ARPES spectra. A) ARPES spectrum along $\bar{Y}-\bar{\Gamma}-\bar{Y}$ path at 20 K. The purple and yellow colors represent the lowest and highest photoelectron intensities, respectively. B) EDCs at various temperatures at kx = 0 Å-1, showing a two-peak structure corresponding to two bands. The peak near the Fermi level shows enhancement of spectral intensity at low temperatures, but negligible above $\approx$125 K. C) Change of the energy position at kx = 0 Å-1 ($\bar{\Gamma}$) with temperature. The top band slightly shifted downward with increasing temperature and no measurable band shift is observed for the bottom band, except for the increase of broadening. D) Change of the energy position at kx = 0.31 Å-1 ($\bar{Y}$) with temperature. The band appears to shift slightly downward with increasing temperature across the magnetic transition. For (C) and (D), the purple and yellow colors represent the lowest and highest photoelectron intensities, respectively. Figure S23:  X-ray photoelectron spectroscopy on bulk TaFe1.14Te3. A) Intensity versus binding energy survey of a bulk sample taken at 298 K with a beam diameter of 100 µm and a source power of 25 W. Ta, Fe, and Te spectral regions are noted with blue, orange, and yellow, respectively. B-D) Intensity versus binding energy focused on expected Ta (B), Fe (C), and Te (D) peak regions. Temperature | 300 K | 200 K | 100 K
---|---|---|---
Empirical Formula | TaFe1.14Te3 | TaFe1.12Te3 | TaFe1.12Te3
Formula weight | 627.42 | 626.02 | 626.58
Temperature | 300.01(10) K | 200.00(10) K | 100.00(10) K
Wavelength | 0.71073 Å | 0.71073 Å | 0.71073 Å
Crystal system | Monoclinic | Monoclinic | Monoclinic
Space group |  P21/m |  P21/m |  P21/m
a | 7.4171(3)Å | 7.4076(3)Å | 7.4105(4)Å
| 90$\circ$ | 90$\circ$ | 90$\circ$
b | 3.63280(10)Å | 3.62530(10)Å | 3.61940(10)Å
| 109.129(5)$\circ$ | 109.175(4)$\circ$ | 109.189(6)$\circ$
c | 9.9740(4)Å | 9.9661(4)Å | 9.9626(5)Å
| 90$\circ$ | 90$\circ$ | 90$\circ$
Volume | 253.908(18)Å3 | 252.789(17)Å3 | 252.37(2)Å3
Z | 2 | 2 | 2
Density (calculated) | 8.207 g/cm3 | 8.225 g/cm3 | 8.246 g/cm3
Absorption coefficient | 41.478 mm-1 | 41.593 mm-1 | 41.690 mm-1
F(000) | 517 | 516 | 516
Crystal size | 0.239$\times$0.049$\times$0.019 mm3 | 0.239$\times$0.049$\times$0.019 mm3 | 0.239$\times$0.049$\times$0.019 mm3
collection range | 2.161$\circ$ to 28.400$\circ$ | 2.164$\circ$ to 28.402$\circ$ | 2.164$\circ$ to 28.539$\circ$
Index ranges | -9$\leq$h$\leq$9,-4$\leq$k$\leq$4,-13$\leq$l$\leq$12 | -9$\leq$h$\leq$9,-4$\leq$k$\leq$4,-13$\leq$l$\leq$12 | -9$\leq$h$\leq$9,-4$\leq$k$\leq$4,-13$\leq$l$\leq$12
Reflections collected | 2966 | 2950 | 2962
Independent reflection | 681 [Rint=0.0410] | 674 [Rint=0.0428] | 682 [Rint=0.0498]
Completeness to =25.242$\circ$ | 100% | 100% | 100%
Refinement method | Full-matrix least-squares on F2 | Full-matrix least-squares on F2 | Full-matrix least-squares on F2
Data/restraints/parameters | 681/0/35 | 674/0/35 | 682/0/35
Goodness-of-fit | 1.082 | 1.121 | 1.047
Final R indices[I$>$2(I)] |  Robs=0.0261, wRobs=0.0601 |  Robs=0.0267, wRobs=0.0578 |  Robs=0.0284, wRobs=0.0627
R indices [all data] |  Rall=0.0291, wRall=0.0624 |  Rall=0.0283, wRall=0.0587 |  Rall=0.0299, wRall=0.0638
Extinction coefficient | 0.0015(3) | 0.0024(3) | 0.0019(3)
Largest diff. peak and hole | 1.725 e$\cdot$Å-3 and -2.003 e$\cdot$Å-3 | 2.093 e$\cdot$Å-3 and -2.263 e$\cdot$Å-3 | 2.136 e$\cdot$Å-3 and -2.824 e$\cdot$Å-3
Table S1:  Crystallographic parameters determined through SCXRD for
TaFe1.14Te3 at various temperatures. R=$|$$|$F0$|$-$|$FC$|$ $|$/$|$F0$|$, wR =
{[w($|$F0$|$2 \- $|$FC$|$2)2]/[w($|$F0$|$4)]}1/2 and
w=1/[2(F02)+(0.021P)2+1.7407P], where P=(F02+2FC2)/3. Growth Batches
---
| EJT-001 | RJ-1-30 | SJH-164 | SJH-171 | SJH-208 | Combined
Ta | 1.00$\pm$0.08 | 0.88$\pm$0.04 | 0.89$\pm$0.06 | 0.85$\pm$0.03 | 0.87$\pm$0.02 | 0.90$\pm$0.06
Fe | 1.21$\pm$0.05 | 1.19$\pm$0.05 | 1.16$\pm$0.06 | 1.26$\pm$0.25 | 1.22$\pm$0.03 | 1.21$\pm$0.04
Te | 3.00 | 3.00 | 3.00 | 3.00 | 3.00 | 3.00
Table S2:  Extracted chemical compositions for multiple TaFe1.14Te3 growth
batches. Relative concentration of Ta, Fe, and Te normalized to the measured
Te concentration for each growth batch. The last column is the average
concentration of each element between all growth batches. Error bars represent
the standard deviation. All chemical concentrations were extracted from
SEM/EDX data. TaFeTe3
---
Non-magnetic | Antiferromagnetic
Element | Charge | Element | Charge | Mag. Moment
Ta | 0.3 | Ta | 0.3 |  $\pm$0.2
Fe1 | 0.4 | Fe1 | 0.5 | 2.2
Fe2 | — | Fe2 | — | —
Te | -0.1 | Te | 0.0 | 0.0
TaFe1.25Te3
Non-magnetic | Antiferromagnetic
Element | Charge | Element | Charge | Mag. Moment
Ta | 0.2 | Ta | 0.3 |  $\pm$0.2
Fe1 | 0.4 | Fe1 | 0.5 | 2.2
Fe2 | 0.4 | Fe2 | 0.5 | 2.3
Te | 0.0 | Te | 0.0 | 0.0
TaFe2Te3
Non-magnetic | Antiferromagnetic
Element | Charge | Element | Charge | Mag. Moment
Ta | 0.2 | Ta | 0.1 |  $\pm$0.1
Fe1 | 0.1 | Fe1 | 0.4 | 2.3
Fe2 | 0.1 | Fe2 | 0.3 | 2.4
Te | 0.0 | Te | -0.1 | 0.0
Table S3:  Calculated Löwdin charge and magnetic moments for TaFe1+yTe3.
Calculated charge and magnetic moment per atom (Ta, Fe1, Fe2, and Te) for
TaFeTe3, TaFe1.25Te3, and TaFe2Te3. Note that due to the arbitrary nature of
atomic orbitals used for projection, the Löwdin charges do not necessarily sum
to zero.