Strain and charge contributions to the magnetoelectric coupling in Fe3O4/PMN-PT artificial multiferroic heterostructures

Abstract

The quest to realize new kinds of data storage devices has motivated recent studies in the field of magnetoelectric heterostructures. One of the most commonly investigated systems is Fe _3 O _4 /[Pb(Mg $_{1/3}$ Nb $_{2/3})$ O _3 ] _0.7 –[PbTiO _3 ] _0.3 (PMN-PT), however, the interplay between different coupling mechanisms is not yet well understood. To disentangle the role of strain and polarisation influence in Fe _3 O _4 /PMN-PT, we report on magnetoelectric coupling measurements for different orientations of the applied magnetic field and for two different substrate cuts, PMN-PT(001) and PMN-PT(011). For Fe _3 O _4 /PMN-PT(011), having the sample aligned such that the magnetic field is parallel to the [01 $\overline{1}$ ] easy axis leads to a remanent increase of the magnetisation for each electric field cycle. On the other hand, for the magnetic field along the [100] hard axis, the magnetisation follows a butterfly-like loop characteristic of strain coupling imparted by the substrate. For Fe _3 O _4 /PMN-PT(001), the magnetoelectric effect is a superposition of the observed behaviour of both in-plane directions in Fe _3 O _4 /PMN-PT(011). The magnetisation shows an initial remanent increase followed by a butterfly like loop. Polarised neutron reflectometry measurements on Fe _3 O _4 /PMN-PT(011) shows no difference between the behaviour at the interface and the bulk of the film and no decline of the interaction further away from the shared interface. Our results demonstrate the role of strain and polarisation on the magnetisation of the Fe _3 O _4 layer and provide a clear step towards the design of future magnetoelectric systems.

Keywords

• thin films
• magnetoelectric coupling
• magnetite
• PMN-PT
• polarised neutron reflectometry
• strain