Investigation of CoPt/M (M = Ag, C) films for high density recording media

In recent years research on high density (> 10 Gbit/in(2)) recording media has been focused on high anisotropy nanocrystalline materials consisting of magnetic nanograins with high coercivity ( > 3 kOe). We have recently star ted a project on CoPt/M (M = Ag, C) with the idea of producing granular sol ids consisting of magnetically hard FCT CoPt particles embedded in Ag and C matrices. The CoPt/Ag films were made in a multilayer form by co-sputterin g from CoPt and Ag targets. The CoPt/C films were deposited by pulsed laser ablation using the focused beam of a KrF eximer laser with fluence of 4 J/ cm(2). The amounts of Ag and C were varied to optimize the magnetic propert ies while reducing particle interactions and therefore signal noise. Films with different layer thickness were made and their structural and magnetic properties were investigated in the as-made state and after annealing in th e temperature range of 500-700 degrees C. Films with Pt content less than 4 0 at% developed the low anisotropy FCC CoPt phase and had a small coercivit y. However, for higher Pt content the anisotropic FCT CoPt phase associated with high coercivity was obtained. In CoPt/C the evolution of FCT phase an d coercivity is rather slow and higher temperature is needed to obtain the right microstructure and high coercivity. Particle size in the range of 5-6 0 nm with corresponding coercivity up to 15 kOe was obtained. The relation among chemical composition, developed microstructure and coercivity are pre sented in this paper. (C) 1999 Elsevier Science B.V. All rights reserved.