Measurement of Curie temperature distribution relevant to heat assisted magnetic recording

Heat-Assisted Magnetic Recording (HAMR) is a likely successor of Perpendicular Magnetic Recording (PMR) in the Hard disk drive industry. In PMR, recording performance is strongly affected by the following distributions in magnetic granular media: magnetic anisotropy field (H-K), volume/grain size, and interaction field from neighboring grains. Since HAMR writing occurs in a narrow temperature region below Curie point (T-c), additional grain-to-grain T-c variation would strongly affect HAMR recording performance. Thus, T-c distribution should be examined for successful HAMR media development. In this paper, we demonstrate a new approach of extracting H-K and T-c distributions (sigma HK and sigma T-c) from thermo-remanence measurements. During the measurement process, a thin film is magnetically saturated, laser heated to specific peak temperature (for a time typically of 5 mu s), then cooled to room temperature and magnetic thermo-remanence is measured. Analytical fit to the experimental curves enables independent evaluation of both sigma T-c (+/- 0.5% absolute) and sigma H-K (+/- 2% absolute). Parameters of the analytical statistical model include: temperature dependencies M-s(T), H-K(T); mean field effective demagnetization factor N; grain size, H-K; and T-c distributions. Thermal fluctuations are taken into account using Arrhenius-Neel formalism. Here, we report experimental sigma T-c values as a function of grain volume. Increase of sigma T-c with grain size reduction might be a limiting factor for HAMR extendibility. (c) 2015 AIP Publishing LLC.