Microstructure and magnetic properties of $L1_0CoPt$ thin film for magnetic recording media

Abstract

Microstructure effects on the magnetic properties of nano-sized $L1_{0} CoPt$ were investigated by intercalating the carbon layer in the form of $CoPt/C_{n}$ (n=0, 1, 4) using RF and DC magnetron sputter deposition. The carbon was observed to dissolve into the ordered CoPt lattice and reduce the ordering kinetics, which results in the reduction of effective crystalline anisotropy constant. The growth of CoPt grains was drastically hindered by the carbon dissolution. The amount of dissolution increases with decreasing carbon single layer thickness due to the capillarity effect. It was found that the grain growth kinetics has a close relationship with the volume fraction of disorderd fcc phase. The grain size of annealed CoPt film was ranging from 30 to 55 nm but CoPt films with additive C showed about 10 nm at n=4 films. CoPt-Ag films deposited at $T_{sub}$=650℃ showed a distinctive microstructure. It was observed that the island-like and discontinuous grains with (110) texture were formed. The (110) texture formation was due to the changes of surface energy and elastic energy upon in-situ ordering transformation. The (110) texture is attributed to the isotropic coercivity. In order to investigate the grain-size distribution, Monte Carlo grain growth simulation and the Weibull function were adapted. It was found that the Weibull function is very useful to know the evolution of microstructure of thin film. When the grain growth occurs as like a 2-D growth system, the Weibull β gives a low value below 3.0 and at this stage the best-fit function of grain-size distribution is not the lognormal function. When the growth occurs as like film thickening, i.e., grains usually grow into film normal direction rather than into in-plane direction, the Weibull β is over 3.0 and the grain-size distribution is following the lognormal distribution. Through temperature dependence (TDC) and angular dependence of coercivity (ADC) of CoPt films and micromagnetic simulations...