近日，课题组和合作者在少层范德华反铁磁体/重金属体系层数依赖自旋霍尔磁电阻效应方面取得进展。相关成果以“Thickness-dependent spin Hall magnetoresistance in few-layer CrPS4/Pt heterostructures”为题发表于英国皇家化学会期刊Nanoscale。

课题组制备了一系列不同厚度的CrPS4/Pt霍尔器件，发现当CrPS4厚度超过8层时，横向电阻中可清晰观察到自旋翻转（spin-flop）相变特征信号，而8层以下该信号逐渐消失。这一现象源于超薄体系中磁各向异性和层间交换耦合的共同减弱。值得关注的是，研究在奈尔温度以上仍观测到显著的反常霍尔信号，该信号在3层超薄器件中依然存在，且可维持至室温。通过对比纯Pt器件的零信号，证实该效应来源于Pt与CrPS4界面的轨道杂化和自旋-轨道耦合增强效应，而非体相CrPS4的本征磁性。此外，角度依赖的纵向电阻测量表明，自旋霍尔磁电阻（spin Hall magnetoresistance, SMR）和各向异性磁电阻的幅值不依赖于CrPS4层数的奇偶性，进一步揭示界面轨道杂化驱动的自旋-轨道散射由SMR机制主导。

该工作为理解低维反铁磁/重金属异质结中的自旋相关输运机制提供了关键实验证据，也为基于少层范德华反铁磁体的新型自旋电子学器件设计奠定了物理基础。

  Recently, our research group and our collaborators made significant progress in studying the layer-dependent spin Hall magnetoresistance effect in few-layer van der Waals antiferromagnet/heavy metal systems. The related findings have been published in Nanoscale, a journal of the Royal Society of Chemistry, under the title 'Thickness-dependent spin Hall magnetoresistance in few-layer CrPS4/Pt heterostructures'.

  We fabricated a series of CrPS4/Pt Hall devices with varying thicknesses. We discovered that when the CrPS4 thickness exceeds 8 layers, a characteristic signal of the spin-flop phase transition can be clearly observed in the transverse resistance. However, this signal gradually disappears below 8 layers. This phenomenon originates from the concurrent weakening of both magnetic anisotropy and interlayer exchange coupling in ultrathin systems. Notably, we still observed a significant anomalous Hall signal above the Neel temperature; this signal persists in ultrathin devices down to 3 layers and can be maintained up to room temperature. By comparing this with the zero signal of pure Pt devices, we confirmed that this effect stems from the orbital hybridization and enhanced spin-orbit coupling at the Pt/CrPS4 interface, rather than the intrinsic magnetism of bulk CrPS4. Furthermore, angle-dependent longitudinal resistance measurements revealed that the amplitudes of both spin Hall magnetoresistance (SMR) and anisotropic magnetoresistance do not depend on the parity of the CrPS4 layer count, further indicating that the spin-orbit scattering driven by interface orbital hybridization is dominated by the SMR mechanism.

  This work provides crucial experimental evidence for understanding spin-dependent transport mechanisms in low-dimensional antiferromagnet/heavy metal heterostructures. It also lays a physical foundation for the design of novel spintronic devices based on few-layer van der Waals antiferromagnets.

图1 少层CrPS4/Pt异质结中纵向SMR的层数奇偶依赖性。(a) 5 K下不同磁场中CrPS4（3层）/Pt器件的SMR。(b) 5 K下不同磁场中CrPS4（8层）/Pt器件的SMR。(c) 5 K和0.5 T条件下不同厚度CrPS4/Pt器件的SMR。(d) 5 K和9 T条件下不同厚度器件的SMR。(e) SMR的层数依赖性。(f) CrPS4（3层）/Pt器件中SMR的磁场依赖性。

论文第一作者为23级硕士研究生许彩琼，共同通讯作者为南洋理工大学丁石磊助理教授和华南理工大学吴锐教授。论文链接：https://pubs.rsc.org/nr/article/18/18/9601/1241855