Kavli Affiliate: Leon Balents
| First 5 Authors: Xiaokang Li, Shan Jiang, Qingkai Meng, Huakun Zuo, Zengwei Zhu
| Summary:
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.
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