Engineering of FePt nanoparticles by e-beam co-evaporation

Abstract

Fe50Pt50 nanoparticles were deposited on thermally oxidized Si substrates byelectron-beam co-evaporation of Fe and Pt, at substrate temperaturesTs between300 and 700 °C. The co-deposition led to the formation of drop-like, coalesced nanoparticles,chain-like structures or continuous films, the morphology being dependent onTs or the nominalthickness of the layer, f. The nanoparticles have a mean diameterDp between 3 and 45 nm, which increases with increasingf. The degree of crystallization in the ordered face centred tetragonal (fct) phase of thesamples depends strongly on the growth conditions and increases with increasingTs andf.Nanoparticles with a higher proportion of the fct phase exhibit higher coercivity, with a maximum value of∼10.3 kOe (for thespecimens prepared at 600 °C with f = 8.5 nm). Conversely, samples with a high proportion of the cubic phase are eithersuperparamagnetic or ferromagnetically soft. The thermal annealing performed on selectedsamples resulted in structural transformation as well as magnetic hardening that depended onf and Dp.