FePt and CoPt nanoparticles co-deposited on silicon dioxide—a comparativestudy

Abstract

We compare CoPt and FePt nanoparticles grown under identical conditions on oxidizedSi substrates by electron beam co-evaporation. Growth was performed under high vacuumconditions at substrate temperatures of 1023 K and was immediately followed by an annealingstep. This process forms CoPt and FePt nanoparticles with mean diameters between∼17 and∼22 nm.In particular, the annealing step results in grain size enlargement for all samples and in a progressivemagnetic hardening of the nanoparticles which reach maximum perpendicular coercivities of∼6.6 kOe (for theCoPt) and ∼10.2 kOe (for the FePt nanoparticles). We show that, during thisannealing step, a progressive transition towards the hard magneticL10 ordered phase takes place in both materials. In contrast to FePt, CoPt nanoparticles mustbe annealed in order to crystallize in this phase.