An Experimental Investigation on Curie Temperature Variations and Related Switching Field Distributions in Heat-Assisted Magnetic Recording Media

The signal-to-noise performance of heat-assisted magnetic recording (HAMR) is closely related to media magnetic and thermal property distribution, especially with the grain-to-grain variations in Curie temperature (T_c) or T_c distribution (σT_c). In this paper, we report an experimental study on T_c variations and related switching field distributions (SFDs) in FePt-based granular HAMR media by a new measurement method using two laser beams [one pump beam for heating and one probe beam for magnetooptical Kerr effect (MOKE) signal detection] and a small perpendicular ac magnetic field (H_sw) applied to the laser heated media. The measured MOKE amplitude (or magnetization) changes with laser power (or media temperature) shows a peak at around T_c, while the full-width-at-half-maximum (FWHM) of the peak is related to the media T_c variations and SFD. The peak position is observed to shift to lower laser power (or media temperature) with broadened FWHM and SFD for larger H_sw. It is demonstrated that the proposed method, being consistent with previous measurement results, is fast and nondestructive. The experimental measurement method and results could provide us quantitative estimations and insights for T_c variations and SFD in HAMR media.