Abstract
In this study, the damping constants of Co/Pt multilayers and hexagonal-closed-packed (hcp) CoPt alloy films are investigated by using a vector network analyzer ferromagnetic resonance spectroscopy (VNA-FMR) and time resolved magneto-optical Kerr effect (TR-MOKE). For Co/Pt multilayer films, very clear linear relationship between FMR frequency and absorption peak width is found. From this relationship, the damping constants of Co/Pt multilayers are evaluated to be about 0.02～0.07 with very small extrinsic contributions. On the other hand, for CoPt alloy films, the absorption peak width becomes wider and exhibits very little FMR frequency dependence. The damping constants of CoPt alloy films evaluated by TR-MOKE, however, are as small as about 0.03～0.06, being almost the same with that Co/Pt multilayers. These discrepancies found in CoPt alloy films can be explained by assuming the large distribution of magnetic anisotropy. Thus the damping constant of CoPt alloy films are some what larger than that of Co/Pt multilayers when these results are compared at same Pt composition.
