Magnetostriction and surface roughness of ultrathin NiFe films deposited on SiO2

Abstract

Ni 81 Fe 19 was sputter deposited onto Si single-crystal wafers which had the native oxide layer intact. Dc hysteresis loops were measured using the magneto-optic Kerr effect, and anisotropy fields determined from the susceptibility. Saturation magnetostriction constants were deduced from the change in anisotropy field as the samples were strained, using the Villari effect. The magnitude of the saturation magnetostriction constant λs of these polycrystalline films was observed to decrease as film thickness was reduced, but always remained negative in sign. Surface roughness was measured using an atomic force microscopy. By considering the variation of the magnitude of the saturation magnetostriction constant with a controlled level of surface roughness, we are able to rule out roughness as the cause of changes in λs as films decrease in thickness below 10–15 nm. This is an important further step in the understanding of the contribution of magnetoelasticity in the performance of soft magnetic films in read heads.