Measurement of Magnetic Properties Relevant to Heat-Assisted-Magnetic-Recording

Heat-assisted magnetic recording (HAMR) is likely the successor of perpendicular magnetic recording (PMR) technology. The quality of HAMR writing is dominated not by the magnetic field gradient (as in PMR), but by the high thermal gradient generated by the laser heating spot. Knowledge of temperature dependence of magnetic parameters: anisotropy field H-k(T), saturation moment M-s(T) and anisotropy field distribution (sigma H-k) in the proximity of Curie temperature (T-c) is crucial for media development. Here we describe a new system to probe the magnetic properties close to T-c, as well as a semianalytical model to explain the results. The model takes into account the thermal fluctuations; input into the model are experimentally measured data for M-s(T), H-k(T), mean field demagnetization factor, sigma H-k and grain size distribution. In the paper we present two types of data: 1) thermal erasure in the absence of a magnetic field; and 2) thermomagnetic writing, allowing the estimate of the switching field distribution at high temperatures.