In-plane strain control of the magnetic remanence and cation-charge redistribution in CoFe₂ O₄ thin film grown on a piezoelectric substrate

Strain engineering of the magnetic property is an important subject in the study of multiferroic materials. Here we propose a multiferroic bilayer structure in which the magnetic remanence is controlled by the in-plane strain of the top CFO (CoFe₂ O₄) layer epitaxially constrained by the bottom Pb (Mg_1/3 Nb_2/3) O₃ -PbTiO ₃ piezoelectric substrate. We have shown that the room-temperature magnetic remanence (MR) of the 100-nm-thick CFO layer is enhanced by 35.4% when an electric field of 10 kV/cm is applied. The MR value of our bilayer structure was shown to be linearly proportional to the magnitude of the in-plane compressive strain which, in turn, was proportional to the applied field strength. Synchrotron x-ray absorption near-edge structure study supports a scenario of the cation-charge redistribution between Co²⁺ and Fe ³⁺ ions under the condition of an electric-field-induced in-plane compressive strain.