Magnetic force microscopy study of magnetic stripe domains in sputter deposited Permalloy thin films

Abstract

A magnetic force microscopy based study on the formation of stripe domains in Permalloy (Ni80Fe20) thin films is presented. Our results show that the critical thickness for stripe domain initiation depended on the sputtering rate, the substrate temperature, and the film thickness. Beyond the stripe domain formation, an increase of the period of a highly ordered array of stripe domains was evident with increasing film thickness. Thin films sputtered at room temperature with thickness variation between ∼80 and ∼350nm exhibited square-root growth dependency on stripe domains periodicity from ∼150to∼380nm, respectively. Above a certain thickness, the domain period decreased and the periodicity deteriorated with the array becoming more random, which is a strong indicator of relatively high structural perpendicular anisotropy. To illustrate, Permalloy sputtered at 100°C initially showed linear dependence in stripe domain periodicity growth up until ∼650nm thick films. The magnetic stripe domain structure began breaking down for thicker Permalloy films. Our data also suggested that the perpendicular anisotropy responsible for the formation of stripe domains might have resulted from strain-caused magnetostriction and the thin-film microstructure shape effect.