Circular magnetic x-ray dichroism in the study of NiFe and AgNiFe thin films

Abstract

Circular magnetic x-ray dichroism (CMXD) has been used as an element specific tool to investigate both AgNiFe heterogeneous alloy and NiFe thin films. The films were rf sputtered at a power of 100 W from a mosaic target in 8 μm of Ar. The absorption and CMXD spectra, recorded at the Ni and Fe L2,3 and L2,3 edges, were measured at station 1.1 of the UK Daresbury Laboratory Synchrotron Radiation Source. For the AgNiFe films, element specific hysteresis loops of both Fe and Ni within the Ag matrix were obtained for several samples in fields of up to 2.5 T. These results clearly showed that the Fe and Ni hysteresis loops superimpose, despite the fact that both the intrinsic anisotropy constants and magnetization of Ni and Fe are very different. This indicates that little or no segregation into elemental Ni or Fe particles occurs in these films. The result adds support to a previously developed phenomenological model of the giant magnetoresistance GMR of such systems, which presumes the existence of discrete NiFe particles. The ratio of the Ni and Fe orbital to spin magnetic moments was also determined for both the AgNiFe and NiFe thin films. The latter were produced by dc sputtering from Ni and Fe targets, and had compositions which varied from 100% Fe to 100% Ni. We find a reasonable correlation between the dependence of the observed m(spin)/m(orbit) ratios as a function of the films composition and previously published data for the gyromagnetic ratio of such films.