Non-Linear Magnetoelectric effects in Hexagonal and Spinel Ferrite Films*

This report is on electric field induced nonlinear magnetoelectric effects (NLME) in single crystals films of spinel and hexagonal ferrites.  The effect manifests as variations in the magnetic order parameters that are proportional to square of the electric field [1,2].  Measurements were carried out on NiZn spinel ferrite, barium and strontium M-type hexaferrites, and Y-type hexagonal ferrite and for electric fields applied either in plane or perpendicular to the film plane.  Ferromagnetic resonance (FMR) in the single domain and multidomain states at 10-58 GHz was utilized to investigate the phenomenon.  The shift in the FMR resonance frequency was measured as a function of input electric power and the data were utilized to estimate the NLME induced changes in the magnetization and anisotropy field.  The shift in FMR frequency and variations in the magnetic parameters were higher in the single domain state than in the multidomain state.  The NLME coefficients estimated from changes in the magnetic parameters were higher for in plane E than for out of plane electric fields.  A phenomenological model for the NLME effect is proposed and qualitatively accounts for the observed dependence of magnetic parameters on input power. The NLME effects in the ferrites are of importance for electrically tunable ferrite microwave signal processing devices.