Factors Influencing Coercive Force Values in Sputtered Permalloy Films

Abstract

Depending upon the experimental conditions used, the mean composition of a sputtered Permalloy film can change progressively with thickness or can be maintained almost constant. In the first case, the extent to which a homogeneous composition is achieved depends upon the ease with which diffusion and mixing can proceed during film growth. It appears that chemical inhomogeneity, resulting from incomplete mixing, leads to the appearance of an anomalous maximum in the plot of wall coercive force Hc versus thickness within the range 600–1000 A. This maximum is similar to that observed in evaporated films and has previously been identified with the transition from Néel to Bloch-type domain walls. The anisotropy coercive force Hk is found to be relatively insensitive to average film composition and homogeneity, but varies systematically with sputtering power and substrate temperature. A similar variation occurs for Hc in those films which are chemically homogeneous, i.e., in which the mean composition remains substantially constant during growth. The equilibrium temperature attained at the substrate after a few seconds and the resulting values of Hk and Hc can thus be effectively controlled by regulating the electrode potential V and current I.