Graduation Year

2004

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Physics

Major Professor

Hariharan, Srikanth.

Keywords

Langmuir-Blodgett, nanoparticles, nanotechnology, ferromagnetism, oxides

Abstract

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.

Ba₀.₅Sr₀.₅Ti₃ (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 < H < 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.

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