Magnetic anisotropy due to pseudo-dipolar interactions in Kitaev-Heisenberg Model

Magnets with strong spin-orbit interactions often have large anisotropic interactions such as Kitaev (pseudo-dipolar) interactions. Such magnets show rich physics related to fluctuations such as spin liquid and order-by-disorder. On the other hand, later studies considering generalized effective models relevant to materials found that these models show rich ground state phase diagram due to the competition between different anisotropic interactions. Therefore, the understanding of the relative strength of anisotropic interactions is necessary for understanding the magnets, as well as to design a material with a desired property. However, there is no experimental method to estimate the strength of anisotropic interactions. In this work, we theoretically discuss the possibility of measuring the Kitaev interaction by magnetic-torque measurement. Focusing on Kitaev-Heisenberg model, we find that the pseudo-dipolar interactions give rise to a magnetic anisotropy with a unique temperature dependence [1]. Furthermore, we find that a linear combination of the magnetic-torque curve only depends on the Kitaev interactions. This allows an experimental observation of the pseudo-dipolar interactions. [1] H. Ishizuka, Phys. Rev. B 95, 184413 (2017).