Well protected SmCo nanoclusters: fabrication and transformation to single crystals

Abstract

Highly pure SmCo nanoclusters (NCs) were prepared by a cluster beam deposition (CBD) method. A very thin (<5 nm) protective layer of carbon (C) was used to protect the nanoclusters from oxidation. No oxygen traces were found even after six months, demonstrating that the pure SmCo NCs can be well protected by a thin C protection layer. This result is of significance for the application of high anisotropy rare earth magnetic nanoparticles. Small size NCs experience diffusion-arbitrated coalescence after deposition causing nonuniform size distribution whereas larger clusters show uniform size distribution. Post-annealing SmCo NCs at 500 °C transforms the structure into the single crystal SmCo₅ phase with hexagonal CaCu₅ symmetry. Higher temperature (≥600 °C) post-annealing causes the structural deterioration of the NCs due to reaction between C and SmCo NCs which is a nanoscale effect and was not observed in bulk counterparts even at 900 °C. The single crystal SmCo₅ NCs have potential applications in high density recording media and permanent magnetic materials. In addition, Sm(Co_0.7Ni_0.3)₅ NCs were also prepared. As-produced Sm(Co_0.7Ni_0.3)₅ NCs were amorphous and crystallized at 500 °C. The coercivity of the crystallized Sm(Co_0.7Ni_0.3)₅ NCs was observed as 1820 Oe. These crystallized NCs might be important for scientific as well as future applications.