Microstructure and Magnetism in Ferrite-Ferroelectric Multilayer Films

Composite magneto-dielectric materials have been investigated over the years because of their potential applications in RF and microwave devices as the dielectric constant and permeability can be individually changed in these materials. In the recent past, there is a renewed interest in systems classified as ferroelectromagnets or multiferroics, which possess simultaneous ferroelectric and magnetic ordering as well as interesting magnetoelastic phenomena. In all these ferrite-ferroelectric materials, the coupling between the permeability (μ) of the magnetically ordered phase and permittivity (e) of the ferroelectric phase make them attractive candidates for multifunctional applications. Ba0.5Sr0.5TiO3 (BSTO) is a ferroelectric with potential applications in tunable filters, antennas, and thin film capacitors. BaFe12O19 (BaF) is a hard ferromagnet with large in-plane anisotropy which makes it promising for use in microwave and RF devices that need permanent magnets for biasing requirements. We have used magnetron sputtering to deposit multilayer films of BSTO and BaF on Al2O3 and heated Si/SiO2. To our knowledge this is the first attempt at combining these technologically important materials in multilayer form. The as-deposited films were amorphous and post-annealing was optimized until distinct BSTO and BaF x-ray peaks could be identified. Surface and images were obtained by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The multilayer structure and BSTO/BaF interfaces were identified using cross-sectional SEM. Magnetic properties of the multilayer films were measured using a Physical Properties Measurement System (PPMS) by Quantum Design at 10K and 300K over a range of magnetic field (0 \u3c H \u3c 7T). We have attempted to correlate some of the magnetic characteristics with the film microstructure. In addition, we have deposited layers of Fe3O4 nanoparticles onto both bare Si/SiO2 substrates and the surfaces of the multilayers using Langmuir-Blodgett technique. Preliminary images of monolayer Fe3O4 particles reveal some ordering present. We have also used the PPMS to look at the magnetic properties of the particles, both by themselves and deposited onto the multilayers to see what magnetic effects the particles have on ferrite-ferroelectric systems