Finite-size effects in ultrafast remagnetization dynamics of FePt

We investigate the ultrafast magnetization dynamics of FePt in the L10phase after an optical heating pulse, asused in heat-assisted magnetic recording. We compare continuous and nano-granular thin films and emphasizethe impact of the finite size on the remagnetization dynamics. The remagnetization speeds up significantlywith increasing external magnetic field only for the continuous film, where domain-wall motion governs thedynamics. The ultrafast remagnetization dynamics in the continuous film are only dominated by heat transportin the regime of high magnetic fields, whereas the timescale required for cooling is prevalent in the granular filmfor all magnetic field strengths. These findings highlight the necessary conditions for studying the intrinsic heattransport properties in magnetic materials.