Magnetic interactions and spin excitations in van der Waals ferromagnet VI$_3$

TL;DR

This study combines DFT and spin-wave theory to analyze magnetic interactions and spin excitations in semiconducting VI3, revealing how dimensionality influences interlayer couplings and the origins of its magnetic anisotropy.

Contribution

It provides a comprehensive analysis of magnetic interactions in VI3 across different forms, including exchange parameters, magnon spectra, and anisotropy, using advanced theoretical methods.

Findings

Intralayer exchange couplings are consistent across monolayer, bilayer, and bulk VI3.

Interlayer couplings vary significantly with dimensionality.

The Curie temperature is estimated using a self-consistent spin-wave approach.

Abstract

Using a combination of density functional theory (DFT) and spin-wave theory methods, we investigate the magnetic interactions and spin excitations in semiconducting VI$_3$. Exchange parameters of monolayer, bilayer, and bulk forms are evaluated by mapping the magnetic energies of various spin configurations, calculated using DFT+$U$, onto the Heisenberg model. The intralayer couplings remain largely unchanged in three forms of VI$_3$, while the interlayer couplings show stronger dependence on the dimensionality of the materials. We calculate the spin-wave spectra within a linear spin-wave theory and discuss how various exchange parameters affect the magnon bands. The magnon-magnon interaction is further incorporated, and the Curie temperature is estimated using a self-consistently renormalized spin-wave theory. To understand the roles of constituent atoms on magnetocrystalline anisotropy energy (MAE), we resolve MAE into sublattices and find that a strong negative V-I inter-sublattice contribution is responsible for the relatively small easy-axis MAE in VI$_3$.