The structure of electroless cobalt alloy films for perpendicular magnetic recording media

Two types of electroless Co alloy films, Co_40.1-Ni_44.2-Re_6.0-P_9.7and Co_23.6-Ni_58.5-Re_5.3-Mn_0.2-P_12.4, were prepared for perpendicular magnetic recording media. The correlation between their structure and magnetic properties was investigated and discussed as a function of film thickness. The magnetic properties of these two types of films showed different patterns of dependence with respect to the film thickness. The Co-Ni-Re-P alloy film gave a higher H_e(⊥) (perpendicular coercivity) in regions where it was very thin; on the other hand, the Co-Ni-Re-Mn-P alloy film displayed a lower H_e(⊥) at the initial film thickness. The composition was observed with AES measurements to be nearly independent of film thickness. The clear columnar structure of both types of films was confirmed by scanning electron microscopy (SEM) and especially by transmission electron microscopy (TEM) observations. Only the reflection high energy electron diffraction (RHEED) patterns for both types of film clearly showed different dependence patterns with respect to the film thickness. The Co-Ni-Re-P film displayed a very highly c-axis oriented structure even at the initial thin film stage. On the other hand, the Co-Ni-Re-Mn-P film showed a dependence of the degree of c-axis orientation on the film thickness, which increased with film thickness. The differences in magnetic properties as a function of thickness were assumed to be due to the degrees of c-axis orientation and change in magnetic domain structure.