Structure Optimization of FePt-C Nanogranular Films for Heat-Assisted Magnetic Recording Media

Systematic investigations for the optimization of FePt-C nanogranular films for heat-assisted magnetic recording media are overviewed. FePt-C films prepared by using compositionally graded process exhibit binomial distribution of grains with a maximum size distribution of 16%. In addition, the average grain size of FePt could be controlled well below 7 nm. Easy-axis distribution can be substantially reduced by growing FePt-C layers on a single crystalline substrate instead of a (001)-textured MgO seed layer, indicating the improvement of (001) texture in the seed layer would reduce the in-plane component. Finite-element micromagnetic simulations incorporating experimentally determined misorientation of FePt grains do not reproduce the experimentally observed demagnetization curve, suggesting the presence of large distribution in the anisotropy fields of FePt grains. A typical growth model of the FePt-C nanogranular films has been proposed on the basis of the thickness-dependent microstructure of the FePt-C nanogranular films, and the suitability of various seed layers has been discussed. The observed results suggest that the suppression of the coarsening of FePt grains is essential to keep the grain size smaller than 6 nm.