Preparation and magnetic properties of CoPt and CoPt:Ag nanocluster films

CoPt and CoPt:Ag nanocluster films have been prepared using a sputtering gas-aggregation cluster source. The cluster size can be controlled in a range from 3 to 8 nm. CoPt cluster films are directly deposited onto Si or 7059 glass substrates. CoPt:Ag cluster films are deposited by co-sputtering or by a CoPt cluster layer with a Ag underlayer and an overlayer. Crystal structure, nanostructure and magnetic properties of the samples were characterized by X-ray diffraction, transmission electron microscopy, and magnetometry. The as-deposited cluster films contain the magnetically soft disordered FCC CoPt phase. Tetragonal L1(0) ordering is realized in the films annealed at a temperature above 650degreesC. The orientation of clusters is generally < 1 1 1 >. The coercivity increases with increase of annealing temperature and annealing time, and very high in-plane and out-of-plane coercivities have been achieved in both CoPt and CoPt:Ag cluster films after annealing at a temperature of 700degreesC for 10 min. The effect of Ag addition on the CoPt:Ag cluster films and the atomic ordering process in these films, and their relations to the hard magnetic properties, is discussed. The preparation of cluster films may provide a new method for fabrication of extremely high-density magnetic recording media. (C) 2003 Elsevier B.V. All rights reserved.