Microstructure and magnetoresistance of Fe-Hf-O films with high electrical resistivity

Fe-Hf-O films composed of bcc-Fe nanograins and an amorphous phase are known as soft magnetic materials suitable for high-frequency use because of their high resistivity. The present paper describes the two different types of magnetoresistive (MR) effect in these films with different compositions. One is the anisotropic MR with a resistivity change, Delta rho, twice as large as that of Ni-Fe films, despite resistivities higher than 10 mu Omega m. The other is the isotropic MR with a surprisingly large Delta rho, three orders of magnitude higher than that of Ni-Fe, which is observed in the Fe-poor (less than or equal to 50 at% Fe) films with even higher resistivities(> 10(3) mu Omega m). This effect is considered to be a tunneling-type granular giant MR due to the spin-dependent tunneling conductance between bcc nanograins through an insulating amorphous phase. The relation between microstructure and MR characteristics is also described.