Memory Erasure and Write Field Requirements in HAMR Using L -FePt Nanoparticles

The write field requirements in heat-assisted magnetic recording (HAMR) using FePt media are studied using an atomistic model. Langevin dynamics simulations of laser-induced thermal demagnetization and magnetization recovery are performed on a single L1_o-ordered FePt grain. We show that the minimum heat temperature for thermal overwrite of information is a cooling ratedependent temperature T_o, larger than the Curie temperature of the grains. If T_o is exceeded, memory effects can be neglected in HAMR since the characteristic pulse time is long compared with the mean first passage time of thermal demagnetization. The minimum write field H_w to attain sufficiently high thermoremanence M_Z = 0.9MS is then independent of the heating process. We study the variation of H_w with cooling rate, damping, field orientation, and grain size L, and explore the phase space of the parameters H, T, and L, also resulting in thermal stability of the recorded information during storage.