Structural and Magnetic Properties of Permalloy Films

Abstract

The wall motion coercive force $H_c$ and the rotational coercive force $H_r$ of thin electroplated nickel‐iron films are studied as a function of film roughness. Three types of roughness are considered : the first, periodic with a wavelength large compared to a domain wall width and an amplitude small compared with the film thickness; the second, of the order of size of a domain wall; and the third, a substrate roughness that is large compared to the film thickness. $H_c$ was found to be related to film thickness according to $H_c{\mathrm{\hspace{0.17em}=\hspace{0.17em}CsD}}^{\mathrm{+n}}$ . This observation was predicted by Néel, except that his assumption of a form of roughness only of the first kind led to a single value for $n$ of $-\frac{4}{3}$ . Electron micrographs showed that roughness of the second kind increased with film thickness, indicating that $n$ depends on this factor. Roughness of the third kind, as introduced by unidirectional polishing, results in an increase of $\mathrm{Cs}$ , while $n$ and $H_r$ are not affected. This third type of roughness was observed to orient the easy magnetic axis parallel to the polishing grooves.