Temperature and Size Dependence of Energy Barrier for Magnetic Flips in L10 FePt Nanoparticles: A Theoretical Study

L10 FePt nanoparticle is among the most promising materials for magnetic recording and nanomagnetic applications. In nanoparticles, the superparamagnetic effect, wherein the thermal fluctuation is comparable to the energy barrier for magnetic flips, strongly affects the stability of magnetic recording. The temperature dependence of the magnetic anisotropy constant in L10 FePt nanoparticles is a crucial factor for estimating the relaxation time of magnetic flips in a magnetic nanoparticle. However, comprehensive simulations of the atomic level for energy barrier for magnetic flips in the L10 FePt nanoparticles are lacking. This study entailed a simulation that quantitatively reproduced the size dependence of the Curie temperature of nanoparticles in the experimental studies. Moreover, the surface effect, wherein the magnetization decreases owing to the loss of magnetic exchange interaction pairs on the surface, was also clarified. The temperature and size dependences of energy barrier for the magnetic flips of L10 FePt nanoparticles were elucidated.