Origin of High Coercivity in Chemically Deposited Cobalt-Phosphorus Films

Films of Co-P, varying in composition from 2.5% to 5% P and varying in thickness from 200 to 2500 Å, were prepared by chemical deposition. The coercivity of these films was found to be a function of both P content and thickness. The particle size of these films increased with increasing thickness and was a function of the P content. The films were annealed in a reducing atmosphere at various temperatures up to 500°C. The low-coercivity films undergo a transformation to films exhibiting coercivities of ∼250 Oe at a temperature of 250°C. The intermediate-coercivity films remain essentially unchanged, whereas the high-coercivity films drop sharply in coercivity at ∼400°C to this apparent ``equilibrium coercivity'' of ∼250 Oe. Etching experiments on these samples show no drastic effects on coercivity. The coercivity merely proceeds back along the original coercivity-versus-thickness curves. Structural and magnetic evidence indicates the existence of an equilibrium magnetic structure in these films which is primarily dependent on particle size.