光磁気メモリー用 CoCr フェライト薄膜のスパッタ生成

抄録

Thin films with the composition of Co_0.8Cr_1.2Fe_1.0O₄ have been rf sputter-deposited at T_s (substrate temperature)=250∼590°C on substrates of quartz glass, SiO₂-coated stainless steel, and aluminum. They were polycrystalline with spinel structure. When 350°C<T_s< 500°C the films exhibited no preferred orientation, while, when T_s>55O°C, they exhibited <111> orientation perpendicular to the film plane. The film deposited on quartz glass had magnetic easy direction parallel to the film plane, while those deposited on stainless steel and aluminum had magnetic easy direction perpendicular to the film plane. This anisotropy may be caused by the internal stress introduced by the difference between the thermal expansion coefficients of the film (α_f) and the substrate (α_s): The films deposited on stainless steel and aluminum have a compressive stress because of α_s>α_f, which results in perpendicular magnetic anisotropy via positive magnetostriction of the film. For the film deposited on stainless steel, the apparent polar Kerr rotation angle including the enhancement by optical interference at SiO₂-underlayer reached as high as 3° at λ=740 nm. This film may be a promising material for magneto-optic memory.