Aging effect on coercivity of iron oxide thin films

Changes in magnetic properties for Fe/sub 3-x//spl square//sub x/O/sub 4/ (x: oxidation degree) thin films made by reactive sputtering and subsequent heat treatments have been examined under room temperature aging and constant temperature annealing. Aging causes variations in coercivity of insufficiently oxidized films which have a specific resistance of less than 1/spl times/10/sup 1/ /spl Omega//spl middot/cm, while the coercivity of /spl gamma/-Fe/sub 2/O/sub 3/ (x=1/3) did not change. This phenomenon did not depend on additive elements or preparation method. Other magnetic properties such as saturation magnetization, residual magnetization, squareness ratio and coercive squareness, were not affected by aging for any Fe/sub 3-x//spl square//sub x/O/sub 4/ composition. The activation energy for a coercivity change is 0.72-0.95 eV near room temperature for films with a specific resistance below 1/spl times/10/sup 1/ /spl Omega//spl middot/cm. It was confirmed that only the coercivity varied at 20/spl deg/C, while both coercivity and the degree of oxidation changed with annealing at 100/spl deg/C.<
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