R&D: Model of Ballistic-Diffusive Thermal Transport in HAMR Media

Japanese Journal of Applied Physics  has published an article written by Andreas Lyberatos, Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Greece, and Gregory J. Parker, Western Digital Company, 3403 Yerba Buena Road, San Jose, California 95135, USA.

Abstract: “A model is presented that considers the grain size and temperature dependence of the thermal conductivity and specific heat of L1₀ FePt nanoparticles and is applied to study the temperature distribution within the top recording layer in heat assisted magnetic recording. Ballistic effects on the thermal conductivity are included assuming diffuse scattering of the electron heat carriers at interfaces and grain boundaries. The magnetic contribution to the specific heat during laser heating close to the Curie temperature is determined using Monte Carlo simulations based on the effective classical spin Hamiltonian of chemically ordered L1₀ FePt. Following the application of a nanosecond laser pulse, the perpendicular heat flow through a FePt/MgO/heat-sink stack is calculated using the finite element method. The temperature drop across the thickness of the FePt layer is shown to be significant for grains of small in-plane size. Size induced grain temperature variations are small due to the temperature dependence of the specific heat of FePt, so the resultant contribution to transition jitter is expected to be limited in extent.“