Magnetic ordering and multiferroicity in MnI$_2$

TL;DR

This study uses density-functional calculations to explore magnetic structures and ferroelectric polarization in MnI$_2$, revealing the importance of inter-plane exchange and spin-orbit coupling in multiferroicity.

Contribution

The paper provides a detailed theoretical analysis of magnetic interactions and polarization in MnI$_2$, aligning with experimental observations and highlighting the role of inter-plane coupling and spin-orbit effects.

Findings

Noncollinear magnetic states are accurately reproduced.

Inter-plane magnetic exchange is crucial for spiral magnetic structure.

Spin-orbit coupling from I ions induces ferroelectric polarization.

Abstract

Density-functional calculations are carried out to investigate incommensurate magnetic structures and ferroelectric polarization in newly discovered multiferroic material MnI$_2$. The exchange interactions among local moments on Mn are parameterized by mapping the mean-field Heisenberg model on to total energy difference of several magnetic ordering states. The experimentally observed noncollinear magnetic states are well reproduced by using this model and exchange interaction parameters. The direction of polarization experimentally measured is also consistent with the result derived from the symmetry analysis of the magnetically ordered state. In particular, we find that the inter-plane magnetic exchange coupling is pivotal to the emergence of the spiral magnetic structure. This noncollinear magnetic structure, combined with spin-orbit coupling mainly from I ions, is responsible for the appearance of ferroelectric polarization.