Theoretical investigation of magnetoelectric effects in Ba2CoGe2O7

TL;DR

This paper combines symmetry analysis and microscopic methods to theoretically investigate magnetoelectric effects in Ba2CoGe2O7, predicting polarization behavior and identifying key microscopic mechanisms.

Contribution

It introduces a comprehensive theoretical framework that explains magnetoelectricity in Ba2CoGe2O7, integrating phenomenological and microscopic approaches.

Findings

Polarization trend under magnetic field can be predicted by Landau theory.

Ba2CoGe2O7 is a prototype magnetoelectric with specific microscopic interactions.

Key mechanisms include spin-orbit coupling and hybridization effects.

Abstract

A joint theoretical approach, combining macroscopic symmetry analysis with microscopic methods (density functional theory and model cluster Hamiltonian), is employed to shed light on magnetoelectricity in Ba2CoGe2O7. We show that the recently reported experimental trend of polarization guided by magnetic field can be predicted on the basis of phenomenological Landau theory. From the microscopic side, Ba2CoGe2O7 emerges as a prototype of a class of magnetoelectrics, where the cross coupling between magnetic and dipolar degrees of freedom needs, as main ingredients, the on-site spin-orbit coupling and the spin-dependent O p - Co d hybridization, along with structural constraints related to the noncentrosymmetric structural symmetry and the peculiar configuration of CoO4 tetrahedrons.