Crystallographic defects in CoCrPt thin film media: effect on interactions and magnetic viscosity

Abstract

We report synchrotron x-ray and magnetic measurements on a set of five CoCrPt thin films, each sputter-deposited onto CrV underlayers after successively increasing the base pressure to which the system was pumped prior to charging with argon. We find that the increase of residual nitrogen gas in the chamber promotes the formation of fcc-like regions in the mainly hcp Co-alloy grains by increasing the stacking fault density. The type and probability of stacking faults were determined from the x-ray data and were found to increase with increasing base pressure, varying from 9% to 30% for samples grown at 10-8 and 10-4 Torr, respectively. These stacking faults cause an increase in regions of low coercivity thus promoting thermally activated magnetization reversal. We have examined the irreversiblemagnetization reversal processes and interactions in detail using remanence, ΔM and magnetic viscosity measurements. ΔM measurements provide a measure of the intergranular interactions. Significant differences were observed in the switching field distributions and ΔM curves. A large increase in activation volume was also observed for films with over 20% stacking faults. We propose that this is due to the reduction in the anisotropy fields caused by the crystallographic defects which then allows exchange coupling to dominate the reversal, causing cooperative reversal. We have also investigated the degree of in- and out-of-plane c-axis texture in the films and find that this is also dependent on the level of nitrogen contamination, as the c-axis texture is very poor in the film grown in the worst vacuum conditions. In the other films we see evidence of some degree of circumferential c-axis texture in the plane of the sample.