Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI3 and CrGeTe3 monolayers

By Changsong Xu, Junsheng Feng, Hongjun Xiang, L. Bellaiche. npj Computational Materials, 2018

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Magnetic anisotropy is crucially important for the stabilization of two-dimensional (2D) magnetism, which is rare in nature but highly desirable in spintronics and for advancing fundamental knowledge. Recent works on CrI3 and CrGeTe3 monolayers not only led to observations of the long-time-sought 2D ferromagnetism, but also revealed distinct magnetic anisotropy in the two systems, namely Ising behavior for CrI3 versus Heisenberg behavior for CrGeTe3. Such magnetic difference strongly contrasts with structural and electronic similarities of these two materials, and understanding it at a microscopic scale should be of large benefits. Here, first-principles calculations are performed and analyzed to develop a simple Hamiltonian, to investigate magnetic anisotropy of CrI3 and CrGeTe3 monolayers. The anisotropic exchange coupling in both systems is surprisingly determined to be of Kitaev-type. Moreover, the interplay between this Kitaev interaction and single ion anisotropy (SIA) is found to naturally explain the different magnetic behaviors of CrI3 and CrGeTe3. Finally, both the Kitaev interaction and SIA are further found to be induced by spin–orbit coupling of the heavy ligands (I of CrI3 or Te of CrGeTe3) rather than the commonly believed 3d magnetic Cr ions.Monolayer magnetism: Kitaev interaction comes into playInterplay between two anisotropic interactions—Kitaev and single-ion—is responsible for magnetism in ferromagnetic thin films. Teams led by Hongjun Xiang at Fudan University in China and Laurent Bellaiche at the University of Arkansas in the US led to the use of first-principles calculations to elucidate magnetic anisotropy in two different two-dimensional ferromagnetic materials with different magnetic behaviors. By developing a predictive Hamiltonian and a tight-binding model, the origin of two-dimensional magnetism in chromium–iodine and chromium–germanium–tellurium monolayers was revealed to be Kitaev interactions and their interplay with single-ion anisotropy. Both the Kitaev and single-ion anisotropies were induced by the spin–orbit coupling of the heavy ligand elements iodine and tellurium. Research into Kitaev interactions in unconventional systems may contribute towards better understanding of interesting physics.

Subfields: Condensed Matter Physics, Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/e9b39db3442802d584aa3506706d45e251136251