Interplay of spin magnetism, orbital magnetism, and atomic structure in layered van der Waals ferromagnet VI3

Recently discovered ferromagnetism of the layered van der Waals material VI3 attracts much research attention. Despite substantial progress, in the following important aspects no consensus has been reached: (i) a possible deviation of the easy axis from the normal to the VI3 layers, (ii) a possible inequivalence of the V atoms, (iii) the value of the V magnetic moments. The theoretical works differ in the conclusions on the conduction nature of the system, the value, and the role of the V orbital moments. To the best of our knowledge there are no theoretical works addressing issues (i) and (ii) and only one work dealing with the reduced value of the V moment. By combining the symmetry arguments with density functional theory (DFT) and DFT-PU calculations we have shown that the antidimerization distortion of the crystal structure reported by Son et al. [Phys. Rev. B 99, 041402(R) (2019)] must lead to the deviation of the easy axis from the normal to the VI 3 layers in close correlation with the experimental results. The antidimerization accompanied by breaking the inversion symmetry leads to the inequivalence of the V atoms. Our DFT-PU calculations result in large value -0.8 mu(B) of the V orbital moments of the V atoms leading to reduced total V moment in agreement with a number of experimental results and with the physical picture suggested by Yang et al. [Phys. Rev. B 101, 100102(R) (2020)]. We obtained large intra-atomic noncollinearity of the V spin and orbital moments revealing strong competition between effects coursed by the onsite electron correlation, spin-orbit coupling, and interatomic hybridization since pure intra-atomic effects lead to collinear spin and orbital moments. Our calculations confirm the experimental results of strong magnetoelastic coupling revealing itself in the strong dependence of the magnetic properties on the distortion of the atomic structure.

Automated summary

The recent discovery of ferromagnetism in the layered van der Waals material VI3 has attracted significant research interest, but issues remain unresolved concerning deviations in the easy axis, inequivalence of V atoms, and V magnetic moments. Utilizing symmetry arguments with DFT and DFT-PU calculations, it has been shown that the distorted crystal structure of VI3 leads to deviations in the easy axis and inequivalence of V atoms. The calculations also reveal a significant intra-atomic noncollinearity of V spin and orbital moments, indicating strong competition between various effects influencing the magnetic properties.