近日，德国马克斯普朗克固体化学物理研究所的Claudia Felser&Subhajit Roychowdhury及其研究团队取得一项新进展。经过不懈努力，他们通过扭曲反铁磁材料中的笼目晶格来增强反常霍尔效应。相关研究成果已于2024年7月15日在国际知名学术期刊《美国科学院院刊》上发表。

该研究团队聚焦于反铁磁（AFM）笼目自旋冰化合物HoAgGe，其晶体结构遵循六方ZrNiAl型，其中Ho原子在扭曲的笼目晶格中排列，于ab平面上构建出独特的金属间笼目自旋冰态。这一非共面结构在约3T的磁场及2.0K的温度条件下，展现出了高达约1.6 μΩ-cm的拓扑霍尔电阻率。

尤为有趣的是，在约45 K（即4倍T_N，T_N约为11 K）时观测到的总反常霍尔电导率（AHC）达到了2800 Ω^-1 cm^-1，这一数值远超HoAgGe作为AFM笼目自旋冰化合物的常规预期，显示出异常特性。研究人员进一步证明，T_N以下的AHC源自外磁场诱导下Weyl点形成的非零贝里曲率；而T_N以上，则主要由笼目自旋引发的倾斜散射机制主导。这些结果为研究AFM笼目晶格化合物的阻挫现象提供了独特的机会。

据悉，在拓扑磁性材料中，电子波函数的拓扑结构与磁序结构是强耦合的。通常而言，铁磁Weyl半金属因其内部存在与磁化强度成正比的巨大贝里曲率，从而产生显著的反常霍尔电导率（AHC）。相比之下，在非共线反铁磁体中观测到的AHC则相对较小。

附：英文原文

Title: Enhancement of the anomalous Hall effect by distorting the Kagome lattice in an antiferromagnetic material

Author: Roychowdhury, Subhajit, Samanta, Kartik, Singh, Sukriti, Schnelle, Walter, Zhang, Yang, Noky, Jonathan, Vergniory, Maia G., Shekhar, Chandra, Felser, Claudia

Issue&Volume: 2024-7-15

Abstract: In topological magnetic materials, the topology of the electronic wave function is strongly coupled to the structure of the magnetic order. In general, ferromagnetic Weyl semimetals generate a strong anomalous Hall conductivity (AHC) due to a large Berry curvature that scales with their magnetization. In contrast, a comparatively small AHC is observed in noncollinear antiferromagnets. We investigated HoAgGe, an antiferromagnetic (AFM) Kagome spin-ice compound, which crystallizes in a hexagonal ZrNiAl-type structure in which Ho atoms are arranged in a distorted Kagome lattice, forming an intermetallic Kagome spin-ice state in the ab-plane. It exhibits a large topological Hall resistivity of ~1.6 μΩ-cm at 2.0 K in a field of ~3 T owing to the noncoplanar structure. Interestingly, a total AHC of 2,800 Ω^-1 cm^-1 is observed at ~45 K, i.e., 4 T_N, which is quite unusual and goes beyond the normal expectation considering HoAgGe as an AFM Kagome spin-ice compound with a T_N of ~11 K. We demonstrate further that the AHC below T_N results from the nonvanishing Berry curvature generated by the formation of Weyl points under the influence of the external magnetic field, while the skew scattering led by Kagome spins dominates above the T_N. These results offer a unique opportunity to study frustration in AFM Kagome lattice compounds.

DOI: 10.1073/pnas.2401970121

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2401970121