Optical Analysis of HAMR Media

We have studied the impact of structural randomness on the variation in optical absorption of recording grains. Using finite-difference time-domain simulation, we demonstrate that randomness in size, shape, and position of FePt grain can cause 2%-9% variation in absorption, depending on the strength of randomness. We have also discussed the resulting impact of several design parameters: air gap, average grain size and its standard deviation, size, and permittivity of grain boundaries, seedlayer thickness, and aspect ratio of recording grains. We demonstrate that the impact of random absorption on jitter is comparable to experimentally estimated variations in Curie temperature σ
_Tc
. In the case of standard recording system parameters, we observe σ
_T
~ 1.5% averaged over the write bubble which corresponds to σ
_T
~ 3% for the grains inside.