Silicide formation and particle size growth in high temperature annealed , self - assembled FePt nanoparticles

High anisotropy, L1 0 , FePt nanoparticle assemblies consisting of 4 nm diameter particles are considered a potential data storage medium beyond 1 Tbit/in 2. However, annealing at temperatures >500°C is required to form the high anisotropy phase. Recently work on the evolution of FePt nanoparticle assemblies as a function of annealing temperature has shown that for T anneal > 650°C a substantial drop in magnetization is observed. Here we show that the observed reduction in magnetization is due to silicide formation as a result of a chemical reaction with the native oxide or Si substrate. We also show that the fraction of particles with L1 0 ordering increases as a function of annealing time with full L1 0 ordering established only after annealing at 725°C for 60mins. We note that particle agglomeration also occurs under these conditions.