Papers by Author: Kazuhiko Ohmori

Abstract: High quality Fe3O4 thin film was synthesized by the magnetron sputtering method using Ar-H2 gas. Giant magneto resistance of the trilayer using Fe3O4 was investigated, where the observed MR ratio was less than 1%. A phenomenological calculation was made to make the origin of the small MR ratio clear, using a parallel current model assuming five passes. It is concluded that the non-magnetic layer surrounded by two magnetic layers is necessary to have the same order resistivity and similar thickness with Fe3O4 layer in order to obtain the large MR ratio for the trilayer using Fe3O4.

Abstract: Annealing effect on the magnetic properties of Fe-Pt nanoparticle was investigated. Fe-Pt nanoparticles were synthesized by the chemical reduction of H2PtCl6 and the decomposition of Fe(CO)5 in the presence of PVP polymers. The samples were annealed at several temperatures from 350°C to 600°C and the structural and magnetic properties were studied by TEM, XRD and magnetization measurements. FePt nanoparticles as-synthesized showed super-paramagnetism and annealed samples at temperatures more than 400°C, ferromagnetism. The crystal structure of as-synthesized sample was disordered fcc, but chemically ordered fct, when it was annealed at more than 400°C. The annealing effects are the concatenation or agglomeration of nanoparticles accompanied with the increase in particle diameter and with the ordering of the FePt superlattice. The critical diameter for emergence of ferromagnetism of FePt particle has been considered to be 3.6 to 5.6 nm in mean diameter, under the existence of the ordered L10 phase The blocking temperature as a function of the annealing temperature was investigated.