Mechanisms of Exchange Bias with MultiferroicBiFeO3Epitaxial Thin Films

Abstract

We have combined neutron scattering and piezoresponse force microscopy to show that the exchange field in $\mathrm{CoFeB}/{\mathrm{BiFeO}}_3$ heterostructures scales with the inverse of the ferroelectric and antiferromagnetic domain size of the ${\mathrm{BiFeO}}_3$ films, as expected from Malozemoff’s model of exchange bias extended to multiferroics. Accordingly, polarized neutron reflectometry reveals the presence of uncompensated spins in the ${\mathrm{BiFeO}}_3$ film at the interface with CoFeB. In view of these results, we discuss possible strategies to switch the magnetization of a ferromagnet by an electric field using ${\mathrm{BiFeO}}_3$.