Sputtered FeHfO films with high electrical resistivity and good soft magnetic properties

Abstract

The microstructures, magnetic properties and electrical resistivities ϱ of FeHfO films with solute content of 2.1–22.7 at.% Hf and 7.8–41.6 at.% O prepared by r.f. magnetron sputtering technique in an ArO 2 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.% ⩽Hf and 5 ⩽ O ⩽ 36 at.% for the as-deposited films. The fraction of the amorphous phase containing a large amount of O, which produces a high ϱ, 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 Fe 54.9Hf 11O 34.1 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 |μ| at 50 MHz of 1800 owing to a high ϱ value of 8 μω m. This value of |μ| for the film 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.