Roig Mercè, Yu Yue, Ekman Rune C, Kreisel Andreas, Andersen Brian M, Agterberg Daniel F
University of Copenhagen, Niels Bohr Institute, DK-2100 Copenhagen, Denmark.
University of Wisconsin-Milwaukee, Department of Physics, Milwaukee, Wisconsin 53201, USA.
Phys Rev Lett. 2025 Jul 2;135(1):016703. doi: 10.1103/839n-rckn.
Altermagnets break time-reversal symmetry, and their spin-orbit coupling (SOC) allows for an anomalous Hall effect (AHE) that depends on the direction of the Néel ordering vector. The AHE and the ferromagnetic spin moment share the same symmetry and hence are usually proportional. However, density functional theory (DFT) calculations find that the AHE exists with negligible ferromagnetic spin moment for some compounds, whereas it reaches sizable values for other altermagnets. By examining realistic minimal models for altermagnetism in which the DFT phenomenology is captured, we uncover a general SOC-enabled quasisymmetry, the uniaxial spin space group, that provides a natural explanation for the amplitude of the ferromagnetic spin moment across the vast range of different altermagnetic materials. Additionally, we derive analytic expressions for the magnetic anisotropy energy, providing a simple means of identifying the preferred Néel vector orientation for altermagnets.
反铁磁体打破了时间反演对称性，其自旋轨道耦合（SOC）会产生反常霍尔效应（AHE），该效应取决于奈尔有序矢量的方向。反常霍尔效应和铁磁自旋矩具有相同的对称性，因此通常成比例。然而，密度泛函理论（DFT）计算发现，对于某些化合物，反常霍尔效应在铁磁自旋矩可忽略不计的情况下依然存在，而对于其他反铁磁体，该效应则达到可观的值。通过研究能够捕捉DFT现象学的反铁磁性实际最小模型，我们发现了一种普遍的由SOC实现的准对称性，即单轴自旋空间群，它为解释各种不同反铁磁材料中铁磁自旋矩的幅度提供了自然的依据。此外，我们推导了磁各向异性能量的解析表达式，为确定反铁磁体首选的奈尔矢量方向提供了一种简单方法。
