[en] Fe₅₀Pt₅₀ nanoparticles were deposited on thermally oxidized Si substrates by electron-beam co-evaporation of Fe and Pt, at substrate temperatures T_s between 300 and 700 deg. C. The co-deposition led to the formation of drop-like, coalesced nanoparticles, chain-like structures or continuous films, the morphology being dependent on T_s or the nominal thickness of the layer, f. The nanoparticles have a mean diameter D_p between 3 and 45 nm, which increases with increasing f. The degree of crystallization in the ordered face centred tetragonal (fct) phase of the samples depends strongly on the growth conditions and increases with increasing T_s and f. Nanoparticles with a higher proportion of the fct phase exhibit higher coercivity, with a maximum value of ∼10.3 kOe (for the specimens prepared at 600 deg. C with f = 8.5 nm). Conversely, samples with a high proportion of the cubic phase are either superparamagnetic or ferromagnetically soft. The thermal annealing performed on selected samples resulted in structural transformation as well as magnetic hardening that depended on f and D_p