Giant Magnetic Anisotropy Induced by Ligand LS Coupling in Layered Cr Compounds

Abstract

We propose a novel origin of magnetic anisotropy to explain the unusual magnetic behaviors of layered ferromagnetic Cr compounds (3d 3 ) wherein the anisotropy field varies from 0.01 T to ∼ 3 T on changing the ligand atom in a common hexagonal structure. The effect of the ligand p orbital spin-orbit (LS) coupling on the magnetic anisotropy is explored by using four site full multiplet cluster model calculations for energies involving the superexchange interaction at different spin axes. Our calculation shows that the anisotropy energy, which is the energy difference for different spin axes, is strongly affected not only by the LS coupling strength but also by the degree of p -d covalency in the layered geometry. This anisotropy energy involving the superexchange appears to dominate the magnetic anisotropy and even explains the giant magnetic anisotropy as large as 3 T observed in CrI3.

Magnetic anisotropy in ferromagnetic CrI3

“…In principle, spin rotational invariance of a 3D magnetic system can be broken via dipolar interactions [10], singleion (magnetocrystalline) anisotropy [11], and/or anisotropic magnetic exchange interactions [12,13]. For layered honeycomb lattice ferromagnet such as CrI 3 [Figs.…”

“…By comparing the temperature dependence of the magnetic anisotropy of CrI 3 with those of CrBr 3 , it was concluded that the magnetic anisotropy in CrI 3 arises from a dominant uniaxial or single-ion anisotropy [24], which comes mostly from the , where the nearest-neighbor I atoms form an octahedral environment with 3 I above (dark purple) and 3 I below (light purple) the Cr layer. The Cr-I-Cr path forms an angle close to 90 degrees [12,13]. The Kitaev interactions between Cr 3+ atoms are marked as J xx , J yy , and J zz [18].…”

“…1(c) and 1(d)]. Since dipolar interactions typically are very small and favor in-plane anisotropy [10], their effects on spin rotation anisotropy are negligible and can be safely ignored [12,13]. On the other hand, single-ion anisotropy in CrI 3 has been estimated to be way below 1 meV because of the quenched orbital moment of Cr 3+ and the large energy separation (≈500 meV) of the CEF excited states of the Cr 3+ ion [Figs.…”

“…On the other hand, single-ion anisotropy in CrI 3 has been estimated to be way below 1 meV because of the quenched orbital moment of Cr 3+ and the large energy separation (≈500 meV) of the CEF excited states of the Cr 3+ ion [Figs. 1(c) and 1(d)] [12,13]. Finally, spin rotational invariance of a magnetic system such as CrI 3 can also be broken because of the magnetic anisotropy arising from the Cr 3d-I p-Cr 3d superexchange hopping in the near 90 • bonding angle networks [ Fig.…”

“…Finally, spin rotational invariance of a magnetic system such as CrI 3 can also be broken because of the magnetic anisotropy arising from the Cr 3d-I p-Cr 3d superexchange hopping in the near 90 • bonding angle networks [ Fig. 1(c)] [12,13].…”