Magnetic Properties and Structure of Cobalt-Platinum Thin Films

Abstract

The magnetic properties of RF sputtered Co-Pt alloy thin films were studied as a function of Pt content from 0 to 80 at%. At room temperature, ferromagnetic films were obtained in the range 0-32 and 40-80 at% Pt. For Pt contents between 32 and 40 at%, discontinuities in the magnetization, magnetostriction, and coercivity versus Pt content were observed; however no discontinuity was observed in the resistivity. The structure of films containing about 25 at%Pt is a mixture of hexagonal and face-centered cubic (FCC) phases. At this composition the magnetostriction is small, but coercivities are large-700 to 2000 Oe-and dependent upon film thickness. The coercivities of these films do not change with heat treatment up to temperatures of 600 °C but decrease markedly at 700 ° C. The properties of equiatomic Co-Pt films are similar to those of bulk alloys. In particular the large coercivity observed in films after heat treatment at 500 ° to 700 °C is due to the formation of an ordered tetragonal phase within the face-centered cubic matrix. The structure of films of about 75 at% Pt is initially a disordered face-centered cubic phase and with heat treatment beginning at 500 ° C an ordered face-centered cubic phase forms. The coercivity of these films (~200 Oe) does not change with annealing at 500 ° C. It decreases slightly upon further annealing at 600 ° to 700 ° C. Electron microscope observations were used to correlate the magnetic properties with film structure. Copyright © 1983 by The Institute of Electrical and Electronics Engineers, Inc.