Opportunities from the nanoworld: Gas phase nanoparticles

In this paper we present studies related to coalescence and oxidation of transition metal nanoparticles with sizes ranging between 2 and 10 nm. For cobalt and iron exposure to air leads to thin oxide shell formation (thickness ≤2 nm), which is thermally unstable upon annealing above ∼200–300 °C. These particles also undergo structural changes due to electron beam stimulated oxidation. However, for molybdenum and niobium the oxide shell is absent and the nanoparticles are stable under electron beam irradiation. Furthermore, for cobalt nanoparticles oxidation leads to a core–shell formation that causes the appearance of an exchange bias field at cryogenic temperatures due to interface ferromagnetic–antiferromagnetic coupling, which is stabilized due to interparticle exchange interactions. The latter also leads to a correlated spin glass state due to its competition with the random intraparticle anisotropy.