The macroscopic monopolization in diagonal magnetoelectrics

TL;DR

This paper introduces a formalism for macroscopic monopolization in periodic solids and explores its connection to the diagonal magnetoelectric effect, supported by first-principles calculations on lithium transition metal phosphates.

Contribution

It develops a theoretical framework for macroscopic monopolization and applies it to specific materials, revealing new insights into their magnetoelectric properties.

Findings

LiMnPO₄ exhibits a ferromonopolar ordering linked to magnetoelectric response.

Other compounds show antiferromonopolar orderings with q-dependent effects.

First-principles calculations quantify contributions to monopolization from magnetic moment distributions.

Abstract

We develop the formalism of the macroscopic monopolization -- that is the monopole moment per unit volume -- in periodic solids, and discuss its relationship to the diagonal magnetoelectric effect. For the series of lithium transition metal phosphate compounds we use first-principles density functional theory to calculate the contributions to the macroscopic monopolization from the global distribution of magnetic moments within the unit cell, as well as from the distribution of magnetization around the atomic sites. We find one example within the series (LiMnPO$_4$) that shows a macroscopic monopolization corresponding to a ferromonopolar ordering consistent with its diagonal magnetoelectric response. The other members of the series (LiMPO$_4$, with M = Co, Fe and Ni) have zero net monopolization but have antiferromonopolar orderings that should lead to $q$-dependent diagonal magnetoelectric effects