Magnetoelectric Interactions in Composites of Ferrite Films on Lattice-Matched Substrates and Ferroelectrics

The nature of the mechanical-strain-mediated converse magnetoelectric effect (CME) is studied in multiferroic composites of single-crystal-like thin films of nickel ferrite (NFO) and polycrystalline lead zirconate titanate (PZT). Ferrite films of thickness 0.45-1 micron are prepared by pulsed-laser deposition on lattice-matched (100)- and (110)-oriented substrates of magnesium gallate (MGO) and cobalt gallate (CGO) that result in elimination of antiphase boundaries and magnetic parameters comparable to bulk single crystals. Ferromagnetic resonance under a static electric field E is utilized for studies of CME effects in composites of PZT and NFO films on the substrates. The in-plane static magnetic field H is applied along the principal crystallographic axes of the ferrite film to study its influence on the CME. The E-induced magnetoelectric (ME) anisotropy field H-ME is estimated from ferromagnetic resonance data based on the shift in resonance frequency with E in order to determine the ME constant A = H-ME/E. In composites with NFO films on (110)-oriented substrates (i) the ME coupling is stronger for films on CGO possibly due to a better lattice match and weaker substrate clamping than for films on MGO, (ii) A values are the highest for H parallel to [1,-1,0], and (iii) a negative A value is inferred for H parallel to [001]. For composites with NFO on (100)-oriented substrates the strongest ME coupling is measured for H along the [001] direction. A model for CME that takes into consideration both compressive and bending deformation in the composites is developed and the results of the theory are in agreement with both the sign and magnitude of the measured ME coefficient A. The results of the studies presented here indicate the potential for use of the composites in self-biased E-tunable microwave devices.