Magnetic properties of perpendicularly orientated L10 FePt nanoparticles

L10 FePt films were deposited on MgO (001) substrates heated to 700°C by magnetron sputtering.Assisted by the misfit of lattice between film and substrate,strong (001) texture was formed.The film at nominal thickness t N=5 nm was composed of nanoparticles with a size of～70 nm,and showed a high coercivity of～105 kOe at 4.2 K.At t N=～50 nm,as the film changed from discontinuous to continuous,the coercivity dropped about one order of magnitude.Micromagnetic simulation implies that the magnetization reversal is a vortex-like nuclear type.The ideal coercivity of a separated single-domain L10 FePt nanoparticle with a size of 70 nm×70 nm×5 nm is～121 kOe.This tells us that the experimental coercivity has nearly reached the limit of ideal single crystalline nanoparticles.