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 beca use of their high resistivity. The present paper describes the two dif ferent types of magnetoresistive (MR) effect in these films with diffe rent compositions. One is the anisotropic MR with a resistivity change , Delta rho, twice as large as that of Ni-Fe films, despite resistivit ies higher than 10 mu Omega m. The other is the isotropic MR with a su rprisingly 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 throug h an insulating amorphous phase. The relation between microstructure a nd MR characteristics is also described.