Abstract
This report is on the observation and theory of electric field E induced non-linear magnetoelectric (NLME) effects in single crystal platelets of ferrimagnetic M-type strontium aluminum hexagonal ferrite. Using microwave measurement techniques, it was found that a DC electric field along the hexagonal c-axis results in significant changes in the saturation magnetization and uniaxial magneto-crystalline anisotropy field and these changes are proportional to the square of the applied static electric field. The NLME effects were present with or without an external bias magnetic field. The E-induced variation in magnetic order parameters is attributed to weakening of magnetic exchange and spin–orbit interactions since conduction electrons in the ferrite are effectively excluded from both interactions while being in transit from one Fe ion to another. We present a phenomenological theory which considers magneto-bielectric effects characterized by a quadratic term in electric field E in the free energy density. The coefficients for the NLME coupling terms have been calculated from experimental data and they do show variations with the Al substitution level and the largest rates of change of the saturation magnetization and anisotropy constant change with the applied power were observed for x = 0.4. It was also clear from the study that strength of the NLME effect does not depend on the amount Al substitution, but critically depends on the electrical conductivity of the sample with the highest NLME coefficients estimated for the sample with the highest conductivity. Results of this work are of importance for a new family of electric field tunable, miniature, high frequency ferrite devices.
Highlights
This report is on the observation and theory of electric field E induced non-linear magnetoelectric (NLME) effects in single crystal platelets of ferrimagnetic M-type strontium aluminum hexagonal ferrite
An important example for device applications for such control is the ability to tune the operating frequency of ferrite devices with an electric field instead of a variable magnetic field produced with a solenoid or an electromagnet that is expected to lead to passive, miniature, lightweight, planar microwave devices with significant reduction in the operating power r equirements[6,7]
We recently reported on the observation of such E-driven NLME effects in pure strontium hexaferrite (SrFe12O19) through measurements on tuning of ferromagnetic resonance (FMR) in the millimeter wave range[32]
Summary
This report is on the observation and theory of electric field E induced non-linear magnetoelectric (NLME) effects in single crystal platelets of ferrimagnetic M-type strontium aluminum hexagonal ferrite. The distinct feature of this concept is the utilization of extremely large current density reaching ≈ 107 A/cm[2] Another approach deals with investigation of electric field (or voltage) effect on magnetic parameters, either directly, or through intermediate elastic s ubsystem[11,12,13]. M-type hexaferrites with collinear spin structure are not multiferroic[28] Such hexaferrites were used as a ferromagnetic phase in a composite with a ferroelectric and the strength of the converse ME coupling measured by electric field tuning of their resonance frequency or field[29,30]. The tuning of the FMR due to NLME was at least 10 times larger than those reported due to linear ME effects in ferrite-ferroelectric c omposites[29,30]
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