Free energy of twisting spins in Mn3Sn
Free energy of twisting spins in Mn3Sn
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DOI：
10.1103/physrevb.106.l020402
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发表时间：
2021-09
影响因子：
3.7
通讯作者：
Xiaokang Li;Shan Jiang;Qi Meng;H. Zuo;Zengwei Zhu;L. Balents;Kamran Behnia
中科院分区：
文献类型：
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作者：
Xiaokang Li;Shan Jiang;Qi Meng;H. Zuo;Zengwei Zhu;L. Balents;Kamran Behnia
磁自由能通常是磁场的二次方，并且取决于磁场和晶轴的相互方向。这种磁晶各向异性能量（MAE）虽然数量级很小，但对于永磁体的存在却是不可或缺的。在这里，我们表明，在 Mn$_3$Sn 这种非共线反铁磁体中，由于发现了其巨大的反常霍尔效应而备受关注，自旋自由能具有超二次分量，从而驱动 MAE。我们通过实验证明，热力学自由能包括磁场中的奇数项 ($\mathcal{O}(H^3)+\mathcal{O}(H^5)$)，并在扭矩响应中产生六倍和十二倍角振荡。我们证明它们可以通过理论进行定量解释，可用于量化系统的相关能量尺度（海森堡、Dzyaloshinskii-Moriya、塞曼和单离子各向异性）。基于该理论，我们得出结论，与普通磁体相比，驱动 Mn$_3$Sn 中 MAE 的是自旋织构的场致变形。
The magnetic free energy is usually quadratic in magnetic field and depends on the mutual orientation of the magnetic field and the crystalline axes. Tiny in magnitude, this magnetocrystalline anisotropy energy (MAE) is nevertheless indispensable for the existence of permanent magnets. Here, we show that in Mn$_3$Sn, a non-collinear antiferromagnet attracting much attention following the discovery of its large anomalous Hall effect, the free energy of spins has superquadratic components, which drive the MAE. We experimentally demonstrate that the thermodynamic free energy includes terms odd in magnetic field ($\mathcal{O}(H^3)+\mathcal{O}(H^5)$) and generating sixfold and twelve-fold angular oscillations in the torque response. We show that they are quantitatively explained by theory, which can be used to quantify relevant energy scales (Heisenberg, Dzyaloshinskii-Moriya, Zeeman and single-ion anisotropy) of the system. Based on the theory, we conclude that, in contrast with common magnets, what drives the MAE in Mn$_3$Sn is the field-induced deformation of the spin texture.