Electroless plated Co alloy films for perpendicular magnetic recording media were investigated as a means of controlling magnetic properties by changing the catalyzing process. In the thin region, such as 500Å thick, a large difference in magnetic properties was shown between the films deposited after acid treatment and with no acid treatment. This was due to the difference in the microstructure of the films. Especially, highly crystallized parts appeared in the grain deposited after acid treatment. The films deposited after acid treatment had high perpendicular coercivity Hc(⊥). Such a high coercivity turned out to be due to these highly crystallized parts. The grain size was controllable with acid treatment which changed the density of active nuclei.
