Magnetic properties of amorphous films of Bi/sub 2/O/sub 3/-Fe/sub 2/O/sub 3/-CaO

The magnetic properties of amorphous films with the composition (Bi/sub 2/O/sub 3/)/sub 0.5-x/(Fe/sub 2/O/sub 3/)/sub 0.5/(CaO)/sub x/ are investigated. Samples with x=0-0.05 were prepared in a pure oxygen or mixed oxygen-argon atmosphere by the RF sputtering technique. As-sputtered films are X-ray amorphous and paramagnetic at room temperature. The films show a spontaneous magnetic moment when annealed in air at temperatures T/sub a/ above 400 degrees C. Data on the room temperature saturation induction 4 pi M with T/sub a/, followed by a maximum in 4 pi M for T/sub a/=600-700 degrees C, depending on the x-value. At higher T/sub a/, a decrease in 4 pi M is observed. The room temperature 4 pi M is found to decrease with increase in x, from 970 G for x=0.1 to 300 G for x=0.5. The Curie temperature is lower than the crystallization temperature. Ferromagnetic resonance studies show a uniaxial or planar anisotropy in the films. X-ray diffraction data do not indicate the precipitation of crystalline ferrimagnetic oxides in the annealed films and the observed magnetization is therefore attributed to ordered amorphous clusters.<
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