Optimization of CoPt/B nanocomposite films for ultrahigh-density recordingmedia

The microstructure and magnetic properties of nanocomposite CoPt/B films ar e investigated in view of their suitability as ultrahigh-density recording media. The as-made films have a disordered face-centered cubic structure an d low coercivity (below 100 Oe). The granular structure is obtained after a n aging heat treatment, which also leads to an increase of the coercivity d ue to the formation of the highly anisotropic face-centered tetragonal phas e. The dynamics of the fct phase formation are found to depend on the boron content. For the sample with 50% vol boron concentration, annealing temper atures as low as 550 degreesC are sufficient to obtain useful coercivities. Transmission electron microscopy studies and x-ray diffraction show that m inimum grain size is obtained for the 20% vol boron concentration for all t emperatures. The "magnetic" grain size is found to coincide with the struct ural only for this particular sample. (C) 2001 American Institute of Physic s.