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].