COERCIVITY AND MICROSTRUCTURE IN CO-PT AND CO-PD THIN-FILMS

Thin films of Co-Pt and Co-Pd have been electrodeposited from alkaline baths based on cobalt amino-citrate complexes and amino-nitrite compl exes of the noble metal, on copper substrates coated with Ni-P ACD (10 mum). Co-Pd films can be obtained in a wide range of compositions; bo th fcc and hcp structures can be present (the last one only for Pd les s-than-or-equal-to 16 at%); the lattice constant varies continously wi th varying composition. The Bragg diffraction peaks are broadened, sug gesting a poorly defined crystalline structure or a high density of de fects. The grains appear to be homogeneous and regular, their size bei ng generally below 100 nm. Co-Pt films are rich in cobalt; they show a fcc structure with a lattice constant varying discontinously and with a (111) PO. A well defined crystalline structure is obtained, with fi ne and regular crystallites (size below 100 nm), and sharp Bragg peaks . Differences in microstructure can be related to large differences in magnetic properties. While Co-Pt films show high coercivities (up to 200 kA/m) and high squareness, Co-Pd films, in the whole range of comp ositions investigated, show very low coercivities and varying squarene ss. In the Co-Pd system, hysteresis cycles sometimes suggest the prese nce of two phases with different micromagnetic behaviours and differen t coercivities; only one of the phases gives the observed value of coe rcivity. We further investigated the effect of layering through pulsed current deposition; the growth of the different phases could be contr olled through control of deposition parameters in the electrodepositio n process. Co-Pd films could be promising candidates for thin-film hea ds in magnetic recording media; their possibilities have not yet been fully assessed, but their magnetic properties, together with their pos sible high corrosion resistance and good mechanical properties, deserv e further studies.