CoPt and FePt nanoparticles for high density recording media

Highly anisotropic CoPt and FePt nanoparticles have been prepared and embedded in a C and BN matrices using the tandem deposition mode. The as-made multilayer CoPt(FePt)/C(BN) films show a disordered face centered cubic (fcc) structure, which is magnetically soft and have low coercivity (<20 Oe). Magnetic hardening occurs after a heat treatment at elevated temperatures (<550°C), which results in the formation of the nanoparticles leading in an increase of coercivity with values up to 15 kOe at room temperature. Transmission electron microscope studies showed FePt particles embedded in C matrix with a size increasing from below 3 nm in the as-made state to about 8 nm in the optimum annealed state. The hardening is due to the high anisotropy of the face centered tetragonal (L1₀) phase with a bulk anisotropy K>10⁷ erg/cm³. The coercivities obtained are much below those expected for noninteracting single-domain particles and the difference is attributed mainly to a smaller anisotropy in the nanoparticles associated with a lower degree of atomic ordering of the L1₀ phase