Effect of bias sputtering on stability of amorphous Tb32Fe68 compositionally modulated thin films

Abstract

We investigated the effect of bias sputtering on the oxidation resistance of amorphous Tb32Fe68 compositionally modulated films (CMFs). The columnar morphologies of aged, unbiased films were more diffused than those of as-deposited films. On the other hand, the morphologies of the −70 V bias sputtered, aged film were as dense and featureless as those of as-deposited films. The substrate bias also influenced the magnetic and magneto-optical characteristics of aged films. The Kerr rotation obtained from the film surface was significantly increased by the formation of a transparent, nonmagnetic oxide layer, and by optical interference between this layer and the unoxidized amorphous matrix. The coercivity of the amorphous matrix in unbiased films increased markedly with aging time. These changes are attributed to compositional changes enhanced by the easy diffusion path of oxygen in the columnar void structure. In contrast, the coercivity of −70 V bias sputtered films was unchanged with aging, and exhibited the B-H loops of exchange coupled double layers. The results indicated that the intrinsic stability of Tb-Fe CMFs was strongly influenced by the film microstructure and was improved by the application of substrate bias during deposition.