Voltage-Tunable High-Frequency Ferrite Devices based on Non-Linear Magnetoelectric Interactions

Oakland University, Rochester MI

Investigators

Abstract

Hexagonal ferrites are magnetic materials of choice for use in high frequency communication devices and radars due to low losses. The main drawback in such devices, however, is the need for a source of magnetic field to tune the operating frequency that requires very high power. Such tuning also makes them bulky and not compatible for integration with semiconductor devices. This project is aimed at a new generation of ferrite magnetic devices that are tunable by applying a voltage, and therefore, can be miniaturized and integrated with semiconductor electronics. The project is motivated by recent reports on strong interaction between the magnetic ordering in the ferrite and electric field generated by the applied voltage, resulting in voltage control of magnetic parameters. Primary tasks of the proposed research are to grow high quality thin films and single crystals of hexagonal ferrites, studies on the nature of interaction between magnetic order and electric field, and design, fabrication and characterization of ferrite filters and resonators for use in the frequency bands of interest for consumer electronics and systems of importance for the national defense. Broader impacts of the research include research training in advanced materials synthesis and measurement techniques for undergraduate and graduate students and research experience for high school students. High school juniors and seniors, women and minorities in particular, will be recruited from local schools to facilitate participation in research. A research program is proposed on non-linear magnetoelectric (NLME) interactions and electric field control of magnetism in M-type hexagonal ferrites. The motivation is the recent discovery of the phenomenon in single crystals films of strontium hexaferrite (SrM). Under a static electric field E, the ME interactions in a thick film of SrM resulted variation in the magnetic order parameters and manifested as tuning of ferromagnetic resonance (FMR). Studies are planned on single crystal platelets and thin films of pure, and (Co, Ti) and (Co,Sn) substituted Ba and Sr hexaferrites. These systems have uniaxial anisotropy fields Ha = 4-20 kOe with FMR in the frequency range 10-50 GHz. Single crystals are on hand and thin films will be grown by liquid phase epitaxy (LPE) on a variety of substrates including MgO and sapphire. Studies on NLME effects are to be done by observation and tuning of FMR under multi-domain and single domain states for DC, sinusoidal and pulsed E-fields. Data on E-tuning of FMR will be used to estimate variations in magnetic order parameters and NLME coupling coefficients and their dependence on sample and input electrical parameters. An important component of the proposed research is the design of hexaferrite resonators and band-stop and band-pass filters for use at 10-50 GHz and characterization in terms of E-tuning and device figures of merit. Avenues for enhancing device tunability and figures of merit and reduction of electric power requirements will be explored. Models will be developed for the non-linear ME interactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.