Fabrication and Control of Magnetic Pd,Fe Thin Film Heterostructures.

Abstract

The goal of this dissertation research is to investigate the use of multiferroic (ferroelectric- ferromagnetic) thin-film interfaces to control the magnetization in materials of interest for perpendicular recording. We explore the relationship between magnetization and structure in thin films of Fe/Pd compounds deposited onto ferroelectric BaTiO3 substrates. Utilizing magnetostrictive coupling, the magnetism of a magnetic film was controlled by the epitaxial strain at the film/substrate interface. BaTiO3 is particularly favorable as it develops a significant elongation along the tetragonal c-axis as a result of symmetry breaking at the cubic to tetragonal phase transition. A novel aspect of the work is to tune the Curie point of the ferromagnetic transition to match the ferroelectric Curie point of the substrate, so that the magnetostrictive effect is maximized. This is achieved by alloying Fe with Pd to produce a Pd3Fe compound. We report for the first time, the elastic control of the perpendicular magnetic anisotropy of Palladium-Iron (Pd,Fe) films deposited onto a barium-titanate (BaTiO3) (100) substrate. Using Magneto-optic Kerr Effect magnetometry, we observed the behavior of the magnetization through the tetragonal-to-cubic phase transition of the BaTiO3 substrate. We found that such films exhibited in-plane magnetization reversal below the T-C transition temperature, and out-of-plane magnetization reversal above the transition. This change in behavior demonstrates the elastic control of the perpendicular magnetic anisotropy of the deposited Pd,Fe film. In addition, we grew an ordered FePd3 film on SrTiO3 using the inter-diffusion of an Fe/Pd multilayer heterostructure. Each layer was deposited using Ultra-High Vacuum deposition. Utilizing in-situ RHEED (Reflection High Energy Electron Diffraction), we observed that each deposited layer was both ordered and exhibited the crystalline structure of the bulk material. Once deposited, the multi-layer heterostructure was heated above the FePd$_{3}$ formation temperature. Upon heating, the RHEED pattern began to exhibit the crystalline structure of FePd3. Using X-ray Diffraction analysis and MOKE magnetometry, we found that the epitaxial film consisted primarily of FePd3. This example of atomic layer epitaxy of Fe, Pd alloys represents a successful approach to forming high quality magnetic heterostructures on perovskites with excellent control over their composition and structural ordering.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120869/1/reneehar_1.pd