Microstratification and stratification in Co-Cr thin films

A number of 1.4 μm thick Co78Cr22films were prepared simultaneously by deposition on glass substrates in a modified Varian DC Magnetron sputtering system. Two ferromagnetic resonance (FMR) responses were seen in the as-deposited wafers: 1) a positive anisotropy "bulk" response and 2) a negative anisotropy "transition region" response. From selected wafers a sequence of thinner films was prepared by ion milling. On the presumption that the films were magnetically stratified, the thicknesses of the bulk and transition layers were calculated from FMR and profilometer data. The data are consistent with the presence of a "transition layer", 96 nm thick, at the glass-film interface. We find that the HKeffvalues of the bulk layer resonance in these films increase with thickness. The FMR line width, ΔH, also increases as film thickness increases from 0.45 μm to 1.4 μm. For films below 0.45 μm in thickness, ΔH increases as the thickness is reduced to that of the transition layer at 0.096 μm. These microstratification effects do not appear to depend critically on whether films of a particular thickness were as-deposited or were thinned down from a thicker specimen. We conjecture that the progressive enhancement of perpendicular anisotropy might be associated with possibly (a) increased c-axis texture with thickness, (b) a perpendicular stress gradient of appropriate sign, (e) a perpendicular Cr concentration gradient of appropriate sign.