Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis

TL;DR

This study uses density functional calculations and classical spin analysis to investigate the magnetic states and ferroelectric polarization of MnWO4, revealing frustrated spin interactions and the origin of its multiferroic properties.

Contribution

It provides a detailed first-principles analysis of magnetic interactions and ferroelectric polarization in MnWO4, clarifying the mechanisms behind its complex magnetic and ferroelectric behavior.

Findings

Spin exchange interactions are frustrated within zigzag chains and between chains.

Spiral-spin order explains incommensurate magnetic state AF2.

Ferroelectric polarization occurs along the b-direction in AF2.

Abstract

The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c-direction and between such chains of Mn2+ ions along the a-direction. This explains the occurrence of a spiral-spin order along the c- and a-directions in the incommensurate magnetic state AF2, and that of a uudd spin order along the c- and a-directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b-direction, in agreement with experiment.