Assessment by FMR of the consequences of etching and annealing in thin Co-Cr films

Previous ferromagnetic resonance (FMR) studies at 30 GHz of sputtered Co-Cr films had indicated the presence of multiple magnetic constituents with differing values of effective magnetic anisotropy. The two resonances seen most often in ∼ 21 at.% Cr specimens had been tentatively associated with (1) a "transition" region (negative anisotropy) at the substrate-film interface, and (2) an upper "bulk" region which, in these relatively high Cr concentration specimens, was characterized by positive anisotropy. We now have performed a sequence of sputter-etching experiments in such films which show that the changes in integrated FMR absorption are indeed consistent with the constituents being configured as layers. Care was taken to avoid annealing during these etching procedures. However, we found when we etched too deeply into the upper bulk layer that annealing of part of the transition region occurred, with subsequent conversion into material with bulk characteristics. An e-beam evaporated film (21 at.% Cr composition) was characterized by FMR by a single constituent with a negative anisotropy of -6.3 KOe. After magnetic annealing for 64 hours at 256° C and at 11.2 KOe an additional positive anisotropy FMR signal was seen at HK=0.9 KOe.