Strain-modulated magnetocapacitance of vertical ferroelectric-ferromagnetic nanocomposite heteroepitaxial films

The strain-mediated magnetocapacitance (MC) of 1-3-type vertical ferroelectric-ferromagnetic nanocomposite films epitaxially grown on different cubic substrates is theoretically calculated using the nonlinear thermodynamic theory combined with elastic theory. The dependences of relative dielectric constant and strain sensitivity of permittivity for the ferroelectric film on the in-plane and out-of-plane misfit strains are obtained. Our results show that the MC effect strongly depends on the in-plane misfit strain and ferromagnetic volume fraction in the nanocomposite films. The calculated MC for the BaTiO3-CoFe2O4 nanocomposite film grown on the SrTiO3 substrate is consistent with the experimental result. Furthermore, a giant MC, which is enhanced by 1-2 orders of magnitude than those reported in experiments, can be obtained for the BaTiO3-CoFe2O4 system grown on the MgO substrate near the transition from the aa-phase to the r-phase. Our result provides a new method for the design of multiferroic nanocomposites with colossal MC effect by optimizing the ferromagnetic phase and substrate types to realize their applications in magnetic-field-controlled electric devices, such as magneto-oscillators, magnetovaractors and magnetoelectric sensors.