Large dynamical magnetic effective charges and anti-magnetoelectricity from spin and orbital origin in multiferroic BiCoO$_3$

TL;DR

This study uses first-principles calculations to analyze the magnetoelectric properties of BiCoO$_3$, revealing anti-magnetoelectric behavior at the linear level and large orbital contributions, with potential for giant responses in ferromagnetic phases.

Contribution

It provides a detailed first-principles analysis of the dynamical magnetic effective charges and magnetoelectric responses in BiCoO$_3$, highlighting the orbital contribution and proposing visualization methods.

Findings

BiCoO$_3$ is anti-magnetoelectric at the linear level.

Orbital contribution to magnetoelectric response exceeds spin contribution.

Ferromagnetic phase exhibits a giant magnetoelectric response of about 1000 ps/m.

Abstract

Using first-principles calculations, we explore the magnetoelectric properties of the room-temperature multiferroic crystal BiCoO$_3$. We use both applied magnetic field and finite-difference techniques to show that BiCoO$_3$ is anti-magnetoelectric at the linear level. The calculation of the dynamical effective charges reveals that the total magnetoelectric response is zero due to the compensating non-zero magnetoelectric response of each magnetic sublattice. This calculation also highlights that the the orbital contribution to the response is remarkably larger than the spin one and that each sublattice has a rather large total magnetoelectric response of 85 ps/m. Furthermore, we provide an intuitive recipe to visualize the dynamical magnetic effective charge, allowing to examine its multipolar nature which we confirm by means of ab initio calculations. Given the large value of the local response, we investigate the ferromagnetic phase as well, which gives a giant magnetoelectric response of about 1000 ps/m and coming mainly from the spin contribution this time. Finally, we discuss the possible reasons for such a large magnetoelectric response in BiCoO3 and propose possible strategies to unveil this potentially large response.