R&D: Composite Media With Reduced Write Temperature for HAMR

Journal of Magnetism and Magnetic Materials has published an article written by N.A.Natekar, Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA, W.Tipcharoen, Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA, and College of Advanced Manufacturing Innovation, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand, and R.H.Victora, Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, USA.

Abstract: “A major issue plaguing Heat Assisted Magnetic Recording (HAMR) is the high writing (T_write) and peak heat spot temperatures (T_peak). To counter this, a low temperature thermal exchange coupled composite (ECC) media with reduced write temperature relative to previous high temperature thermal ECC media is introduced. The FePt T_c is reduced from 700K to 500K, and the write layer T_c is reduced from 900K to 600K. Optimizations for M_s and K_u of the write layer generate values of M_s = 700 emu/cm³ and K_u = 1.0 × 10⁷ erg/cm³ at 300K. Switching Probability Distribution (SPD) calculations with lowered T_peak = 650K indicate T_write = 487K. This indicates a T_write reduction by 34% as compared to the previous write temperature of 738K for the high temperature thermal ECC media. Examining the FWHM of the SPD under 0% and 3% T_c variation indicates a noise reduction of ∼20% relative to single layer high T_c FePt media, and a much larger reduction relative to low T_c FePt media. The jitter values at lowered T_c approach the ideal value set by the grain size in the absence of any T_c and K_u variation. Simulations with uncorrelated and correlated T_c and K_u variations in the write and FePt layer generate similar results. Reduction of FePt T_c may reduce the anisotropy relative to its undoped value: reduction of anisotropy by 33% is found to adversely affect the SPD by only 3-4%, but has a larger impact on jitter. These results help establish the usefulness of a low temperature thermal exchange coupled composite media for HAMR.“