Systems with magnetically ordered two-dimensional (2D) layers bound by van der
Waals (vdW) interaction are getting increasingly interesting for high-tech magneto-electric and magneto-optic applications in nanostructures. Due to their intrinsic magnetocrystalline anisotropy, several vdW magnets could be thinned down to nanoscale thickness, while still maintaining magnetic order. A prominent example of such materials are transition metal trihalides, in particular CrI3, a first atomically thin ferromagnet [1].
Here we focus on trihalides VI3 and VBr3. VI3 is a ferromagnet whose monolayer critical temperature is even slightly higher than that of its bulk form, TC = 60 K. VBr3 is expected to be a layered antiferromagnet. VI3 exhibits a rather unusual magnetic anisotropy [2]. First-principles calculations show its strong connection to the lattice, namely they reproduce the magnetic anisotropy only if lattice distortions present at the low temperature phase are taken into account [3]. The calculations converge to two strikingly different solutions: either a ground state with quenched orbital momentum, typical for 3d transition metals, or a ground state with an exceptionally high orbital momentum [3,4]. The latter solution could explain the strong coupling between lattice and magnetism, as well as the disagreement between the calculated spin momentum and the measured magnetic momentum per V site. Predicted electronic configurations are compared to recent measurements based on the x-ray magnetic circular dichroism
[1] B. Huang, et al., Nature 546, 270 (2017).
[2] A. Koriki et al., Phys. Rev. B 103, 174401 (2021).
[3] L. M. Sandratskii, K. Carva, Phys. Rev. B 103, 214451 (2021).
[4] K. Yang, F. Fan, H. Wang, D.I. Khomskii, H. Wu , Phys. Rev. B 101, 100402 (2020).