Persistence of large and gate-tunable anisotropic magnetoresistance in an atomically thin antiferromagnet

Abstract: Anisotropic magnetoresistance (AMR) offers a robust electrical readout of antiferromagnetic (AFM) states, playing a central role in the rapidly advancing field of AFM spintronics. Despite its great versatility, electrical probing of the Néel vector via AMR remains challenging in the ultrathin limit due to interface disorder and reduced dimensionality. Here, we demonstrate electrical readout of the Néel vector down to 1.3 nm (two layers) in the two-dimensional van der Waals (vdW) AFM semiconductor NiPS3. Leveraging spin-flop-mediated rotation of the Néel vector and using both transistor and tunnel-junction device geometries, we identify two distinct AMR contributions in NiPS3, that dominate at low and high charge densities, respectively. We achieve full gate control over these contributions, enabling tunability of both the magnitude and sign of magnetoresistance. Our results establish semiconducting vdW antiferromagnets as a rich platform for studying AMR in the ultrathin limit, opening new avenues for multifunctional AFM spintronic devices.

• The paper establishes persistent gate-tunable AMR in NiPS3, achieving electrical readout of the Néel vector down to a 1.3 nm bilayer limit.
• It employs both lateral FET and vertical tunnel junction architectures to distinctly probe crystalline and noncrystalline AMR contributions under variable gating.
• The study benchmarks NiPS3 as a superior 2D antiferromagnetic semiconductor for scalable spintronic devices with high magnetoresistance magnitude.

Electrical Readout of Atomically Thin AFM Order in NiPS3 via Gate-Tunable Anisotropic Magnetoresistance

Introduction

Anisotropic magnetoresistance (AMR) in antiferromagnets (AFMs) is a key modality for electrical characterization of magnetic order. The recent proliferation of two-dimensional (2D) van der Waals (vdW) antiferromagnets has enabled investigation of AMR at the atomic scale, which is critical for developing spintronic devices with enhanced miniaturization and novel functionalities. The AFM semiconductor NiPS3, with robust in-plane magnetic order and higher carrier mobility than chromium trihalides, represents a promising candidate for such investigations (2604.15793). However, probing AMR in ultrathin AFM layers has remained a challenge due to interface disorder and reduced dimensional stability. This work demonstrates persistent, gate-tunable AMR down to bilayer (1.3 nm) thickness in NiPS3, delineates distinct AMR contributions arising from crystalline and noncrystalline origins, and establishes direct electrical readout of the Néel vector in the 2D limit.

Experimental Approach and Device Architectures

The authors fabricated both lateral field-effect transistor (FET) and vertical tunnel-junction devices using multilayer NiPS3, graphite contacts, and h-BN encapsulation. Magnetotransport measurements were performed with in-plane magnetic fields, leveraging the spin-flop transition to rotate the Néel vector. FET devices probed in-plane transport, while tunnel junctions accessed the out-of-plane regime. Monoclinic stacking and intrinsic uniaxial anisotropy permitted angular control of the Néel vector, and the device geometry enabled independent manipulation of angles relevant to crystalline (relative to crystal axes) and noncrystalline (relative to current) AMR.

Characterization of AMR Contributions

Analysis of magnetoresistance (MR) as a function of magnetic field orientation and gate voltage revealed two distinct AMR mechanisms:

• Noncrystalline AMR: Dominant at high gate voltages (electron density $\gtrsim 3 \times 10^{12}$ cm$^{-2}$), the MR is maximized when current aligns parallel to the Néel vector and is minimized when perpendicular, with positive AMR sign. This response is analogous to ferromagnetic systems and is governed by the orientation between electrical current and staggered magnetization.
• Crystalline AMR: Emergent at low charge density (near transistor threshold), MR depends on the angle between the Néel vector and the crystallographic easy axis. This regime is electrically accessible via gating, and in tunnel junction geometry, MR originates exclusively from crystalline AMR, independent of current direction.

A crossover between noncrystalline and crystalline AMR regimes was extracted quantitatively by fitting MR data to a two-component angular model. Full gate control over magnitude and sign of MR was achieved, enabling electrical isolation of the underlying mechanisms.

Ultrafine Thickness Limit and Layer Scaling

Measurements down to bilayer NiPS3 (1.3 nm) showed that AMR (both magnitude and tunability) persists unchanged through the ultrathin limit. Comparison across thicknesses revealed that AMR magnitude is effectively thickness-independent in lateral geometry, and the signal demonstrates no observable degradation upon thinning. NiPS3 is benchmarked as the thinnest functional AFM channel exhibiting electrical AMR, with MR exceeding that of conventional AFM systems such as CuMnAs and Mn2Au, which suffer signal loss in ultrathin films due to interface scattering and disorder. Further, AMR values in vertical tunnel junctions are maximized due to the low charge density regime.

Mechanistic Interpretation

The authors propose that at high doping, positive noncrystalline AMR reflects enhanced resistivity when carriers propagate along ferromagnetic zig-zag chains—the canonical AMR in ferromagnetic systems driven by anisotropic scattering. At low densities, spin-orbit interaction induces a shift in conduction band minimum as the Néel vector rotates away from the easy axis, reducing barrier height in tunnel devices and increasing thermally activated carrier density in FETs, hence leading to negative MR. The vdW structure of NiPS3 suppresses interface disorder and stabilizes AFM order at the atomic scale.

Practical and Theoretical Implications

These findings have significant implications for AFM spintronics:

• Device Functionality: Electrical readout of the Néel vector, gate-tunable AMR (sign and magnitude), and persistence of MR down to the bilayer limit establish the viability of multifunctional, scalable 2D AFM devices.
• Mechanistic Dissection: The ability to independently probe crystalline and noncrystalline AMR contributions through gate control provides a platform for systematic investigation of scattering mechanisms in AFMs.
• Material Benchmarking: NiPS3 outperforms metallic AFM systems in both thickness scaling and MR magnitude, attributed to its semiconducting nature and layered structure.
• Future Directions: Insights into magnetotransport at the atomic scale underpin development of tunable memory elements, ultrafast AFM spintronic circuits, and AFM opto-spintronics leveraging semiconducting coupling to light.

Conclusion

This study establishes persistent, electrically tunable AMR in atomically thin NiPS3, enabling robust electrical readout of AFM order and delineating distinct crystalline and noncrystalline contributions controllable via gate voltage. These results bridge the gap between fundamental AFM magnetotransport and practical device engineering, positioning vdW AFM semiconductors as a foundational platform for next-generation spintronic technologies (2604.15793).