The effect of heat-treatment on magnetic properties and microstructure of electroless CoNiP films for perpendicular magnetic recording media was investigated in order to clarify the microstructure in as-deposited conditions, as well as to evaluate their thermal stability. The as-deposited film consisted of a mixture of <002> perpendicularly oriented hcp structure and fcc structure without obvious crystal orientation. The heat-treatment higher than 400°C altered the crystal structure from the domination of the hcp structure into that of the fcc structure. The crystallites grow larger with the heat-treatment, causing a sharp change in the magnetic properties. These changes were due to the disappearance of magnetocrystalline anisotropy induced by the cobalt hcp structure, and the decrease in the shape magnetic anisotropy due to the change in film topology. On the basis of these results. it was suggested that a compositional inhomogeneity due to a segregation of Co-rich region existed in the as-deposited films; then such segregated conditions disappeared by the heattreatment, thus the crystal property of the film changed into the fcc one.
