Magnetoelectric effect in mixed valency oxides mediated by charge carriers

TL;DR

This paper demonstrates that free charge carriers in mixed-valence oxides can induce multiferroic behavior by mediating interactions among spins and dipoles, with an optimal carrier concentration maximizing the magnetoelectric effect.

Contribution

It introduces a mechanism where charge carriers mediate multiferroic order in mixed-valence oxides, highlighting the role of carrier concentration and disorder effects.

Findings

Existence of an optimal carrier concentration for maximum ME interaction.

Charge carriers can mediate multiferroic behavior via spin and dipole interactions.

Disorder does not suppress the multiferroic effects in these materials.

Abstract

We show that the presence of free carriers in a substance can generate the multiferroic behavior. Namely, if the substance has mixed-valence ions, which can supply free carriers and have electric dipole and spin moments, all three types of long-range order (ferromagnetic, ferroelectric and magnetoelectric (ME)) can occur at low temperature. The physical origin of the effect is that charge carriers can mediate the multiferroic behavior via spin - spin (RKKY), dipole-dipole and dipole - spin interactions. Our estimate of the interaction magnitude shows that there exist an optimal carrier concentration, at which the strength of ME interaction is maximal and comparable to that of spin-spin RKKY interaction. This permits to conclude that in substances, where RKKY interaction between local spins is not small, a substantial value of free carriers mediated ME interaction can occur. Our analysis shows that disorder in the above substances does not suppress multiferroic effects.