Enhancement of coercivity in nanometer-size CoPt crystallites

In this study, we showed that a magnetic coercivity (H-c) as high as 37 kOe was obtained in a CoPt thin film that contains separated nanometer-size Co Pt crystallites. We prepared CoPt thin films with thicknesses of 5 and 175 nm by magnetron sputtering. After annealing in an Ar/H-2 atmosphere at temp eratures from 650 to 750 degrees C for 3-12 h, we measured the magnetic pro perties and found that magnetic H-c relates to annealing temperature, annea ling time and film thickness. From atomic force microscopy and magnetic for ce microscopy studies, the magnetic single domain size of CoPt is in the ra nge of 100-200 nm. The high H-c is likely due to the well-separated nanomet er-size crystallites and the well-ordered fct phase of CoPt alloy. (C) 1999 American Institute of Physics. [S0021-8979(99)51108-0].