SPUTTERED FE-HF-O FILMS WITH HIGH ELECTRICAL-RESISTIVITY AND GOOD SOFT-MAGNETIC PROPERTIES

The microstructures, magnetic properties and electrical resistivities rho of Fe-Hf-O films with solute content of 2.1-22.7 at.% Hf and 7.8-41.6 at.% 0 prepared by rf. magnetron sputtering technique in an Ar-O2 mixed atmosphere were investigated. A structure composed of a b.c.c. phase and an amorphous phase is found to be formed in the compositional range 10 at.% less-than-or-equal-to Hf and 15 less-than-or-equal-to O less-than-or-equal-to 36 at.% for the as-deposited films. The fraction of the amorphous phase containing a large amount of O, which produces a high rho increases the size of the b.c.c. grains decreases with increasing Hf content. The films with an O-to-Hf ratio of 3.2-4.0 show low coercivities of 30-100 A m-1 in the as-deposited state and also good soft magnetic properties after annealing under optimum conditions which do not cause a substantial change in the as-deposited structure. An Fe54.9Hf11O34.1 film annealed for 21.6 ks at 673 K in a rotating field of 160 kA m-1 exhibits a B(s) of 1.2 T, an H(c) of 64 A m-1 and a Absolute value of u at 50 MHz of 1800 owing to a high rho value of 8 muOMEGA m. This value of Absolute value of u for the films is superior to those for already-known metallic soft magnetic films. Therefore the Fe-Hf-O films are expected to be useful for the core material of micromagnetic devices in the high frequency range.