Mechanisms of exchange bias with multiferroic BiFeO3 epitaxial thin films

TL;DR

This study investigates how the exchange bias in CoFeB/BiFeO3 heterostructures relates to the multiferroic domain structure of BiFeO3 films, revealing the scaling behavior and interface spins, with implications for electric-field control of magnetization.

Contribution

It demonstrates the scaling of exchange bias with domain size in multiferroic BiFeO3 and identifies uncompensated spins at the interface, extending Malozemoff's model to multiferroics.

Findings

Exchange bias scales with inverse domain size.

Uncompensated spins are present at the interface.

Potential for electric-field control of magnetization.

Abstract

We have combined neutron scattering and piezoresponse force microscopy to study the relation between the exchange bias observed in CoFeB/BiFeO3 heterostructures and the multiferroic domain structure of the BiFeO3 films. We show that the exchange field scales with the inverse of the ferroelectric and antiferromagnetic domain size, as expected from Malozemoff's model of exchange bias extended to multiferroics. Accordingly, polarized neutron reflectometry reveals the presence of uncompensated spins in the BiFeO3 film at the interface with the CoFeB. In view of these results we discuss possible strategies to switch the magnetization of a ferromagnet by an electric field using BiFeO3.