Akihiro Makino and Yasuo Hayakawa
Nagaoka Branch, Central Laboratory, Alps Electric Co., Ltd., Nagaoka
Fe--Hf--O films with solute contents of 2.1 to 22.7 at.%Hf and 7.8 to 41.6 at.%O were prepared by a r.f. magnetron sputtering apparatus in Ar+O2 atmosphere, and their microstructures, magnetic properties and electrical resistivities (ρ) were investigated. A structure composed of an amorphous and a bcc phases is found to be formed in the compositional range of 10 at.%≤qHf and 15≤qO≤q 36 at.% for Fe--Hf--O films. The fraction of the amorphous phase containing a large amount of O which produces high ρ, increases and the size of the bcc grain decreases with increasing Hf content. The crystallization of the amorphous phase takes place through two stages, at the lower- and higher-temperature above 730 K, due to the precipitation or growth of the bcc phase and the oxide phases containing Fe or Hf, respectively. The films with the compositional range of (O/Hf)=3.2~ 4.0 in the as-deposited state show low coercivities of 30~ 100 A/m and also excellent soft magnetic properties after annealing at 673 K which cause the substantial change of the as-deposited structure. Fe54.9Hf11O34.1 film annealed at 673 K for 21.6 ks in a rotating magnetic field of 160 kA/m exhibits a low coercivity (Hc) of 64 A/m, a high magnetization (Bs) of 1.2 T and a high permeability (|μ|) of 1800 at 50 MHz due to its high electric resistivity (ρ) of 8× 10-6 Ω⋅m, the value of |μ| is superior to those for known soft magnetic materials. It is therefore expected that the films with good soft magnetic properties in addition to high ρ is useful for micro magnetic devices at the high frequency range.
(Received July 3, 1993)
iron--hafnium--oxygen system, sputtered film, amorphous phase, bcc phase, nanoscale grain structure, crystallization, high magnetization, high electrical resistivity, high permeability
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