Oxidation Studies of CoCr Thin Films for Use as Magnetic Media

Oxidation studies using AES and XPS techniques have been performed on CoCr thin films containing 20 at.% Cr. Samples exposed to air and vacuum at different temp. and to boiling water have been studied. Auger sputter depth profiles indicate that on exposure to air Cr enrichment occurs at the surface of the film. Chromium content at the surface of the film and the depth at which the bulk composition is reached increase with the temp. of exposure. Samples heated in vacuum show little enrichment. The Cr enrichment in air is attributed to its greater affinity for oxygen. Samples immersed in boiling water exhibit a surface Cr content that is comparable to sample heated in air at 400 deg C. However, the depth at which bulk composition is reached is only a third of the 400 deg C sample. This indicates that water more readily oxidizes Cr than air and that the oxidation is diffusion limited. XPS analyses indicate that the oxides formed are CoO and Cr sub 2 O sub 3 . Sputter depth profiles show that CoO is always accompanied by Cr sub 2 O sub 3 , while Cr sub 2 O sub 3 may be accompanied by metallic Co, once again indicating the preferential oxidation of Cr over Co. 8 ref.--AA