Antiferromagnetic Transition Temperature Research Articles

Annealing-Tunable Charge Density Wave in the Magnetic Kagome Material FeGe.

The unprecedented phenomenon that a charge density wave (CDW) emerges inside the antiferromagnetic (AFM) phase indicates an unusual CDW mechanism associated with magnetism in FeGe. Here, we demonstrate that both the CDW and magnetism of FeGe can be effectively tuned through postgrowth annealing treatments. Instead of the short-range CDW reported earlier, a long-range CDW order is realized below 110K in single crystals annealed at 320 °C for over 48h. The CDW and AFM transition temperatures appear to be inversely correlated with each other. The onset of the CDW phase significantly reduces the critical field of the spin-flop transition, whereas the CDW transition remains stable against minor variations in magnetic orders such as annealing-induced magnetic clusters and spin-canting transitions. Single-crystal x-ray diffraction measurements reveal substantial disorder on the Ge1 site, which is characterized by displacement of the Ge1 atom from the Fe_{3}Ge layer along the c axis and can be reversibly modified by the annealing process. The observed annealing-tunable CDW and magnetic orders can be well understood in terms of disorder on the Ge1 site. Our study provides a vital starting point for the exploration of the unconventional CDW mechanism in FeGe and of kagome materials in general.

Modulation of the Structural, Magnetic, and Dielectric Properties of YMnO3 by Cu Doping.

The lower valence compensation of YMn1-xCuxO3 (x = 0.00, 0.05, and 0.10) is prepared by the solid-state reaction, and the effects of divalent cation Cu-doping on the construction and magnetic and dielectric attributes of multiferroic YMnO3 are systemically researched. Powder X-ray diffraction shows YMn1-xCuxO3 has a single-phase hexagonal construction with a P63cm space group as the parent YMnO3, and lattice parameters decrease systematically as Cu concentration increases. Using the scanning electric microscope, structure morphologies analysis shows that the mean grain size varies between 1.90 and 2.20 μm as Cu content increases. YMn1-xCuxO3 magnetization increases as Cu doping concentration increases, and the antiferromagnetic transition temperature declines from 71 K for x = 0.00 to 58 K for x = 0.10. The valence distributions of Mn ions conduce to the modified magnetic attributes. Due to Cu substitution, the dielectric loss and dielectric constant decline as frequency increases from 400 to 700 K, showing representative relaxation behaviors. Indeed, that is a thermally activated process. In addition, the peak of the dielectric loss complies with the Arrhenius law. The relaxation correlates to the dipole effect regarding carrier hopping between Mn3+ and Mn4+, and also correlates to oxygen vacancies generated by Mn2+.

The multiferroic properties of Pb3Fe2F12

Fluoride ferroelectrics containing 3d transition metal ions are potential multiferroic candidates due to their ionic bonds rather than the covalent bonds in oxide ferroelectrics. In this work, Pb3Fe2F12 ceramics are prepared by solid-state reaction. Rietveld refinement of the x-ray diffraction pattern suggests that Pb3Fe2F12 adopts a crystalline structure similar to that of Pb5Fe3F19, containing FeF6 octahedra chains and isolated FeF6 octahedra. The deficiency of Pb content leads to the mixed valence states of Fe ions and strong distortion among the octahedra, thus, complicating exchange interactions between Fe ions. The antiferromagnetic transition temperature TN1 is observed at 160 K, which is significantly higher than that of stoichiometric Pb5Fe3F19. Various magnetic anomalies are observed at low temperatures due to the onset of different antiferromagnetic exchange interactions between Fe ions of different strengths with TN2 (∼45 K), TN3 (∼37 K), and TN4 (∼10 K). Weak ferromagnetism can be observed below TN2, and significant exchange bias is observed below TN4. Dielectric peaks, together with a magnetic field tunable pyroelectric current peak, are observed at around TN1, suggesting the multiferroic nature and magnetoelectric coupling in Pb3Fe2F12.

Pressure-induced magnetic phase and structural transition in SmSb2

Abstract Motivated by the recent discovery of unconventional superconductivity around a magnetic quantum critical point in pressurized CeSb2, here we present a high-pressure study of an isostructural antiferromagnetic (AFM) SmSb2 through electrical transport and synchrotron x-ray diffraction measurements. At P C ~2.5 GPa, we found a pressure-induced magnetic phase transition accompanied by a Cmca→P4/nmm structural phase transition. In the pristine AFM phase below P C, the AFM transition temperature of SmSb2 is insensitive to pressure; in the emergent magnetic phase above P C, however, the magnetic critical temperature increases rapidly with increasing pressure. In addition, at ambient pressure, the magnetoresistivity (MR) of SmSb2 increases suddenly upon cooling below the AFM transition temperature and presents linear nonsaturating behavior under high field at 2 K. With increasing pressure above P C, the MR behavior remains similar to that observed at ambient pressure, both in terms of temperature- and field-dependent MR. This leads us to argue an AFM-like state for SmSb2 above P C. Within the investigated pressure of up to 45.3 GPa and the temperature of down to1.8 K, we found no signature of superconductivity in SmSb2.

Critical enhancement of the spin Hall effect by spin fluctuations

The spin Hall (SH) effect, the conversion of the electric current to the spin current along the transverse direction, relies on the relativistic spin-orbit coupling (SOC). Here, we develop a microscopic theory on the mechanisms of the SH effect in magnetic metals, where itinerant electrons are coupled with localized magnetic moments via the Hund exchange interaction and the SOC. Both antiferromagnetic metals and ferromagnetic metals are considered. It is shown that the SH conductivity can be significantly enhanced by the spin fluctuation when approaching the magnetic transition temperature of both cases. For antiferromagnetic metals, the pure SH effect appears in the entire temperature range, while for ferromagnetic metals, the pure SH effect is expected to be replaced by the anomalous Hall effect below the transition temperature. We discuss possible experimental realizations and the effect of the quantum criticality when the antiferromagnetic transition temperature is tuned to zero temperature.

Magnetism, heat capacity, magnetocaloric effect, and magneto-transport properties of heavy fermion antiferromagnet CeGaSi

We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility, specific heat and electrical resistivity measurements as well as high pressure effect. Magnetic measurements reveal that an antiferromagnetic order develops below T m ∼ 10.4 K with magnetic moments orientated in the ab plane. The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states. The max magnetic entropy change −ΔSMmax (μ 0 H⊥c, μ 0 H = 7 T) around T m is found to reach up to 11.85 J⋅kg−1⋅K−1. Remarkably, both the antiferromagnetic transition temperature and −lnT behavior increase monotonically with pressure applied to 20 kbar (1 bar = 105 Pa), indicating that much higher pressure will be needed to reach its quantum critical point.

Site preference of the 3[formula omitted] transition metal ions in the Mn[formula omitted]Fe[formula omitted]Nb[formula omitted]O[formula omitted] compounds as revealed by Mössbauer spectroscopy

In this paper, we report on structural, magnetic, Mössbauer spectroscopy and density functional theory (DFT) studies of the Mn4−xFexNb2O9 compounds. Temperature dependent magnetization measurements have shown that the paramagnetic to antiferromagnetic transition temperatures, TN, depend non-linearly on the Fe doping level x, which is different from earlier studies on similar compounds of Mn4−xCoxNb2O9. More interestingly, our Mössbauer spectroscopy measurements have revealed preferential occupation of the 3d transition metal ions, namely, the Fe(Mn) atoms prefer to occupy the highly buckled M-II(relative flat M-I) site, which can be well understood by the band mixing behavior from our DFT calculations. These results are expected to be important for a better understanding of the rich physics of this family of compounds, especially when one concerns the interpretation of experimental results of similar mixing compounds.

The impact of A-site cations on the crystal structure and magnetism of the new double perovskites ALaCoTeO6 (A = Na and K).

In this work, we report the structural and magnetic characterization of two new B-site rock-salt ordered double perovskites ALaCoTeO6 (A = K+ and Na+) with mixed A-site cations. KLaCoTeO6 crystallizes in the space group P4/nmm with a long-range ordering degree of 84.8% for the A-site K+/La3+ cations, whereas NaLaCoTeO6 adopts an unexpected triclinically distorted I1̄-structure with Na/La3+ disordering, validated by combined Rietveld refinements against high-resolution neutron diffraction data and Cu Kα1 X-ray powder diffraction data. Magnetic susceptibility at low temperatures shows clear antiferromagnetic (AFM) transitions for both compounds. KLaCoTeO6 exhibits the highest AFM transition temperature of 20 K amongst all the Co/Te-ordered 3C-type A2CoTeO6 (A = Pb2+, Sr2+, and Ca2+) and ALaCoTeO6 double perovskites due to its larger Co2+-O-Te6+ bond angle and A-site cationic ordering-induced larger distortion of the Co2+-based face-centered cubic sublattice. Moreover, we found that the average radius of the A-site cations plays a decisive role in the AFM transition temperatures of all these ordered double perovskites, that is, a larger A-site cation always results in a higher AFM transition temperature. This provides a strategy to subtly manipulate the magnetic properties of ordered double perovskites.

Elucidating the Magnetoelastic Coupling, Pressure-Dependent Magnetic Behavior, and Anomalous Hall Effect in FexTi2S4 Intercalation Sulfides.

Transition-metal chalcogenides with intercalated layered structures are interesting systems in material physics due to their attractive electronic and magnetic properties, with applications in the fields of magnetic refrigerators, catalysts, and thermoelectrics, among others. In this work, we studied in detail the structural, electronic, and magnetic properties of (Fe,Ti)-based sulfides with formula FexTi2S4 (x = 0.24, 0.32, and 0.42), prepared as polycrystalline materials under high-pressure conditions. They present a layered Heideite-type crystal structure, as assessed by synchrotron X-ray diffraction. A local structure analysis using Fe K-edge extended X-ray-absorption fine structure (EXAFS) data unveiled a conspicuous contraction of the main Fe-S bond in Fe0.24Ti2S4 at the vicinity of the magnetic transition 60-80 K. We suggest that this anomaly is related to magnetoelastic coupling effects. The EXAFS analysis allowed extraction of the Einstein temperatures (θE), i.e., the phonon contribution to the specific heat, for the two bond pairs Fe-S(1) [θE ≈318 K; 290 K (C/T)] and Fe-Ti(1) [θE ≈218 K; 190 K (C/T)]. In addition to the structural and local vibrational measurements, we probed the magnetic properties using magneto-calorimetry, magnetometry under applied pressure, magnetoresistance (MR), and Hall effect measurements. We observed the appearance of a broad peak in the specific heat around 120 K in the x = 0.42 compound that we associated with an antiferromagnetic ordering electronic transition. We found that the antiferromagnetic transition temperature is pressure and composition sensitive and reduces at 1.2 GPa by ∼12 and ∼3 K, for the members with x = 0.24 and x = 0.42, respectively. Similarly, the saturation magnetization in the ordered phase depends on both pressure and iron content, reducing its value by 50, 90, and 30% for x = 0.24, 0.32, and 0.42, respectively. We observed clear jumps in the magnetic hysteresis loops, MR, and anomalous Hall effect (AHE) below 2 K at fields around 2-4 T. We associated this observation with the metamagnetic transitions; from the Berry-curvature a decoupling parameter of SH = 0.12 V-1 is determined. Comparison of the results on the temperature-dependent magnetization, MR, and AHE elucidates a strong inelastic scattering contribution to the AHE at higher temperatures due to the cluster spin-glass phase.

Flux Growth and Raman Spectroscopy Study of Cu2CrBO5 Crystals

Multicomponent flux systems based on both Li2WO4-B2O3-Li2O-CuO-Cr2O3 and Bi2O3-MoO3-B2O3-Na2O-CuO-Cr2O3 were studied in order to grow Cu2CrBO5 crystals. The conditions for Cu2CrBO5 crystallization were investigated by varyingthe component ratios, and the peculiarities of their interaction were characterized by studying the formation sequence of high-temperature crystallizing phases. Special attention was paid to the problem of Cr2O3 solubility. Phase boundaries between CuCrO2, Cu2CrO4, and Cu2CrBO5 were considered. The crystal structure of the obtained samples was studied viasingle crystal and powder X-ray diffraction. The chemical composition of the grown crystals was examined using the EDX technique. Anactual ratio of Cu:Cr = 1.89:1.11 was found for Cu2CrBO5 grown from the lithium-tungstate system, which showed a small deviation from 2:1, implying the presence of a part of bivalent Cr2+ in the samples. Anomalies in the thermal dependence of magnetization were analyzed and compared with the previously obtained data for Cu2CrBO5. The anomaly at TC ≈ 42 K and the antiferromagnetic phase transition at TN ≈ 119 K were considered. Polarized Raman spectra of Cu2CrBO5 were obtained for the first time, and a comparative analysis of the obtained data with other monoclinic and orthorhombic ludwigites is presented. Along with the polarized room temperature spectra, the thermal evolution of Raman modes near the antiferromagnetic phase transition temperature TN ≈ 119 K is provided. The influence of the magnetic phase transition on the Raman spectra of Cu2CrBO5 is discussed.

Ni-doping assisted modification of the non-collinear antiferromagnetic ordering in Mn5Si3 alloy

Ni-doped Mn5Si3 alloys of nominal compositions Mn5−xNixSi3 (for x = 0.05, 0.1, and 0.2) have been investigated through detailed neutron powder diffraction (NPD) studies in zero magnetic field and ambient pressure. At room temperature, all three Ni-doped alloys crystallize with D88 type hexagonal structure having P63∕mcm space group. These alloys undergo paramagnetic → collinear antiferromagnetic → non-collinear antiferromagnetic transitions on cooling from room temperature. A significant decrease in collinear to non-collinear antiferromagnetic transition temperature has been observed with increasing Ni concentration. The magnetic structure of both antiferromagnetic phases can be described by the magnetic propagation vector k = (0,1,0). However, the moment size and the orientation in the non-collinear antiferromagnetic phase are found to be notably affected by the Ni-doping. Approaching near-parallel arrangement of Mn-moments with increasing Ni-doping is found to be responsible for the gradual disappearance of unusual magnetic properties (inverted hysteresis loop, thermomagnetic irreversibility, etc.) observed in Mn5Si3 alloy.

Enhanced coercivity and emergent spin-cluster-glass state in 2D ferromagnetic material, Fe[formula omitted]GeTe[formula omitted

Two-dimensional (2D) van der Waals (vdW) magnetic materials with high coercivity and high TC are desired for spintronics and memory storage applications. Fe3GeTe2 (F3GT) is one such 2D vdW ferromagnet with a reasonably high TC, but with a very low coercive field, HC (≲100 Oe). Here we present a phase-engineered sample of F3GT with enhanced coercivity (7–10 times), without compromising its fundamental magnetic properties (TC≃ 210 K). The parent F3GT phase is infused with a small percentage of randomly embedded clusters of a coplanar FeTe (FT) phase, which serves as both mosaic pinning centers between grains of F3GT above its antiferromagnetic transition temperature (TC1∼ 70 K) and also as anti-phase domains below TC1. As a result, the grain boundary disorder and metastable nature are greatly augmented, leading to highly enhanced coercivity, cluster spin glass, and meta-magnetic behavior. The enhanced coercivity (≃1 kOe) makes F3GT-2 much more useful for memory storage applications.

Antiferromagnetic order and its interplay with superconductivity in CaK(Fe1−x Mn x )4As4

The magnetic order for several compositions of CaK(FeMn x )4As4 has been studied by nuclear magnetic resonance (NMR), Mössbauer spectroscopy, and neutron diffraction. Our observations for the Mn-doped 1144 compound are consistent with the hedgehog spin vortex crystal (hSVC) order which has previously been found for Ni-doped . The hSVC state is characterized by the stripe-type propagation vectors and just as in the doped 122 compounds. The hSVC state preserves tetragonal symmetry at the Fe site, and only this SVC motif with simple antiferromagnetic (AFM) stacking along c is consistent with all our observations using NMR Mössbauer spectroscopy, and neutron diffraction. We find that the hSVC state in the Mn-doped 1144 compound coexists with superconductivity, and by combining the neutron scattering and Mössbauer spectroscopy data we can infer a quantum phase transition, hidden under the superconducting dome, associated with the suppression of the AFM transition temperature (T N) to zero for x ≈ 0.01. In addition, unlike several 122 compounds and Ni-doped 1144, the ordered magnetic moment is not observed to decrease at temperatures below the superconducting transition temperature (T c).

Structural and magnetic interplay in multiferroic Ho0.5Nd0.5Fe3(BO3)4

Rare-earth iron borates, $R{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ ($R$ = rare earth), are of considerable interest because of their structural and magnetic complexities due to the involvement of both $3d$ and $4f$ magnetic interactions in a helical lattice. Among them ${\mathrm{Ho}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ has attracted the most attention, as it exhibits a multiferroic property with a large, spontaneous, and magnetic-field-induced electric polarization ($P$) below the antiferromagnetic transition temperature (${\mathrm{T}}_{N}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}32$ K). This compound has been reported to be noncentrosymmetric (nonpolar) down to the lowest temperature, and the origin of spontaneous electric polarization below ${\mathrm{T}}_{N}$ is not known. By utilizing temperature-dependent synchrotron x-ray powder diffraction, we report here the observation of structural phase transition, i.e., the lowering of crystal symmetry from $R32$ to $P{3}_{1}21$ below ${\mathrm{T}}_{N}$ in ${\mathrm{Ho}}_{0.5}{\mathrm{Nd}}_{0.5}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$, which is further confirmed by single-crystal x-ray diffraction measurements as well as substantiated by dielectric and Raman spectroscopic results. With the help of x-ray resonant magnetic scattering, we have studied the element-specific magnetic ordering behavior, and by combining all the results, we show that the spontaneous electric polarization below the antiferromagnetic ordering transition emerges through the p-d hybridization mechanism associated with the ${\mathrm{FeO}}_{6}$ octahedra. The observations of subtle structural changes at low temperature and element-specific magnetic ordering behavior provide a comprehensive understanding of the multiferroicity in this family of compounds.

Chemical pressure effects on Tm1-yRyMn0.3Co0.7O3 due to element substitution at A-site

To clarify the chemical pressure effects on TmMn0.3Co0.7O3 due to element substitution at an A-site, the crystal structure and magnetic properties of Tm1-yRyMn0.3Co0.7O3 (R = Y and Lu) were investigated. All the prepared samples possessed a perovskite-type orthorhombic structure with the Pnma space group, and the unit-cell volume V increased with the average radius of A-site ions 〈rR〉. From the effective magnetic moment Peff and M−H measurements, it was found that the electronic states of the ions in the samples were Tm3+, Mn4+, Co2+(high-spin state, S = 3/2), and Co3+(low-spin state, S = 0). The physical parameters including the canted antiferromagnetic transition temperature Tc increased with V. The field-cooled magnetization MFC below 30 K could be explained by the antiferromagnetic interaction between the paramagnetic Tm and the 3d metal sublattices. Since Tc and the fitting parameter of this two-sublattice model increased with V, these changes were considered to be attributed to the chemical pressure generated by element substitution at the A-site.

Doping-induced spin reorientation and magnetic phase diagram ofEuMn1−xZnxSb2 (0≤x≤1)

${\mathrm{EuMnSb}}_{2}$ is an intriguing magnetic topological semimetal containing two antiferromagnetic sublattices, and the interplay of magnetism between Eu and Mn sublattices leads to rich interesting transport phenomena. Here we report a comprehensive experimental study of the magnetic properties in ${\mathrm{EuMn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Sb}}_{2}$ (0 $\ensuremath{\le}x\ensuremath{\le}$ 1) by using structural, resistivity, magnetization, and specific heat measurements. The magnetic phase diagrams of ${\mathrm{EuMn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Sb}}_{2}$ along two magnetic field orientations are established based on magnetization and specific heat measurements, constituted by the antiferromagnetic ordering of Mn at high temperature, and successive magnetic transitions of Eu at low temperatures. The antiferromagnetic transition temperature of Mn is suppressed by Zn doping and cannot be detected by specific heat measurements when $x>$ 0.3. The antiferromagnetic transition temperature of Eu exhibits a weak nonmonotonic doping dependence with a significant anisotropy in the doping range of 0 $\ensuremath{\le}x\ensuremath{\le}$ 0.4. The spin orientation of Eu is gradually reoriented from the out-of-plane direction to the in-plane direction. It closely correlates with the Mn antiferromagnetic ordering, indicating a strong coupling between the Eu and Mn magnetism. Our study will be helpful for understanding the magnetic properties of compounds with two antiferromagnetic lattices and open an avenue for tuning the spin orientation through the interaction between the different magnetic lattices.

Evidence of Long-Range and Short-Range Magnetic Ordering in the Honeycomb Na3Mn2SbO6 Oxide

We present a comprehensive study of the synthesis, structure, and magnetic properties of the honeycomb oxide Na3Mn2SbO6 supported by neutron diffraction, heat capacity, and magnetization measurements. The refinements of the neutron diffraction patterns (150, 50, and 45 K) using the Rietveld method confirm the monoclinic (S. G. C2/m) structure. Temperature-dependent magnetic susceptibilities measured at varying fields along with the heat capacity measurements demonstrate the coexistence of long-range ordering (∼42 K) and short-range ordering (∼65 K). The field-dependent isothermal magnetization measurements at 5 K indicate a spin-flop transition around 5 T. Rietveld refinements of the low-temperature (below 45 K) neutron diffraction data further confirm the long-range magnetic ordering. In addition, the temperature variation of the lattice parameters obtained from the neutron powder diffraction analysis exhibited a distinct anomaly near the antiferromagnetic transition temperature. The appearance of the concomitant broadened backgrounds in the neutron powder diffraction data collected at 80, 50, and 45 K supports the short-range ordering. The resultant magnetic structure consists of spins that are aligned antiparallel with the nearest neighbors and also with the spins of the adjacent honeycomb layers. The occurrence of a fully ordered magnetic ground state (Neel antiferromagnetic (AFM)) in Na3Mn2SbO6 consolidates the significance of fabricating new honeycomb oxides.

Observation of Electronic Structure Modification in the Hidden Order Phase of CeCoSi

CeCoSi with no local inversion symmetric crystal structure (P4/nmm) exhibits a phase transition of unknown origin (Hidden Order: HO) at about 12 K (T0) above the antiferromagnetic transition temperature (TN = 9.4 K). The electronic structure change across T0 was investigated with high-precision optical reflection spectroscopy. The optical spectrum changed from a typical metallic behavior above T0 to a gap-like structure at around 15 meV below T0. The gap-like structure was unchanged across TN except for the narrowing of the Drude component of carriers due to the suppression of magnetic fluctuations. This result suggests a slight change from the typical metallic electronic structure above T0 to that with an energy gap near the Fermi level in the HO phase. The change in electronic structure in the HO phase was concluded to be due to electron/valence instability.

Nonreciprocity of Optical Absorption in the Magnetoelectric Antiferromagnet CuB2O4

The change in the absorption spectra due to reversal of the direction of light propagation (nonreciprocity of absorption) is a consequence of a simultaneous violation of both time-reversal and spatial-inversion symmetries. Here, we report on a high-resolution spectroscopic study of absorption nonreciprocity in the noncentrosymmetric multiferroic CuB2O4 below the antiferromagnetic transition temperature TN = 21 K in the commensurate phase in magnetic fields up to 0.5 T. The study was performed in a broad spectral region covering several exciton transitions, which all are followed by an anomalously rich structure due to the multiple exciton-magnon-phonon satellites. Two components were resolved for the spectral line near 1.4 eV corresponding to the exciton transition between the ground and the first excited state. A quantitative theory of the optical absorption and nonreciprocity at this line was developed. The theory takes into account the interference between the electric and magnetic dipole contributions to the absorption and gives an adequate explanation of the relevant effects.

Electrical Interrogation of Thickness‐Dependent Multiferroic Phase Transitions in the 2D Antiferromagnetic Semiconductor NiI2

Abstract2D magnetic materials hold promise for quantum and spintronic applications. 2D antiferromagnetic materials are of particular interest due to their relative insensitivity to external magnetic fields and higher switching speeds compared to 2D ferromagnets. However, their lack of macroscopic magnetization impedes detection and control of antiferromagnetic order, thus motivating magneto‐electrical measurements for these purposes. Additionally, many 2D magnetic materials are ambient‐reactive and electrically insulating or highly resistive below their magnetic ordering temperatures, which imposes severe constraints on electronic device fabrication and characterization. Herein, these issues are overcome via a fabrication protocol that achieves electrically conductive devices from the ambient‐reactive 2D antiferromagnetic semiconductor NiI2. The resulting gate‐tunable transistors show band‐like electronic transport below the antiferromagnetic and multiferroic transition temperatures of NiI2, revealing a Hall mobility of 15 cm2 V−1 s−1 at 1.7 K. These devices also allow direct electrical probing of the thickness‐dependent multiferroic phase transition temperature of NiI2 from 59 K (bulk) to 28 K (monolayer).