Surprisingly oxidation resistant icosahedral FePt nanoparticles showing hard-magnetic properties have beenfabricated by an inert-gas condensation method with in-flight annealing. High-resolution transmission electronmicroscopy (HRTEM) images with sub-Angstrom resolution of the nanoparticle have been obtained withfocal series reconstruction, revealing noncrystalline nature of the nanoparticle. Digital dark-field methodcombined with structure reconstruction as well as HRTEM simulations reveal that these nanoparticles haveicosahedral structure with shell periodicity. Localized lattice relaxations have been studied by extracting theposition of individual atomic columns with a precision of about (0.002 nm. The lattice spacings of (111)planes from the surface region to the center of the icosahedra are found to decrease exponentially with shellnumbers. Computational studies and energy-filtered transmission electron microscopy analyses suggest thata Pt-enriched surface layer is energetically favored and that site-specific vacancies are formed at the edges offacettes, which was experimentally observed. The presence of the Pt-enriched shell around an Fe/Pt coreexplains the environmental stability of the magnetic icosahedra and strongly reduces the exchange couplingbetween neighboring particles, thereby possibly providing the highest packing density for future magneticstorage media based on FePt nanoparticles.

We have synthesized firework-like Co2P nanostructures using a simple and reliable thermal decomposition route with the precursors, triphenyl phosphine and cobalt acetylacetonate, in oleylamine. The optimized reaction temperature is within a narrow window around 280 _C. The nanostructures have a firework-like morphology with nanoneedles growing out of a center core. The nanoneedles are single crystals with clean surfaces, about 200 nm in length, and a tapering tip less than 10 nm in diameter. These nanostructures exhibit Curie–Weiss PM behavior with the effective moment determined as 2.46 mB per FU. Based on the synthesis designs with detailed characterizations on the intermediates at different stages of the phase formation, the growth mechanism of the firework-like Co2P nanostructures is proposed. It is feasible to apply this method of synthesis for some of the other transition-metal phosphide nanostructures.