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 started a project on CoPt/M (M = Ag, C) with the idea of producing granular solids 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-sputtering 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 properties 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 the temperature range of 500-700 degrees C. Films with Pt content less than 40 at% developed the low anisotropy FCC CoPt phase and had a small coercivity. However, for higher Pt content the anisotropic FCT CoPt phase associated with high coercivity was obtained. In CoPt/C the evolution of FCT phase and coercivity is rather slow and higher temperature is needed to obtain the right microstructure and high coercivity. Particle size in the range of 5-60 nm with corresponding coercivity up to 15 kOe was obtained. The relation among chemical composition, developed microstructure and coercivity are presented in this paper. (C) 1999 Elsevier Science B.V. All rights reserved.