Structure and magnetic properties of Co/CoO and Co/Si core-shell cluster assemblies prepared via gas-phase

Plasma-gas condensation cluster deposition systems have been introduced and applied for preparation of Co/CoO and Co/Si clusters assemblies. In Co/CoO cluster assemblies prepared by the single source PGC system with introduction of O2 gas into the deposition chamber, fcc Co cores are covered with NaCl type CoO shells, showing marked enhancement of unidirectional and uniaxial magnetic anisotropy and a clear cross-over phenomenon in the magnetic relaxation from the high temperature thermal regime to the low temperarure quantum tunneling regime. In Co/Si cluster assemblies prepared by the double source PGC system, fcc Co cores are also covered with amorphous Si rich shells, showing rather small magnetic coercivity. Since Co/CoO and Co/Si core-shell clusters are stable in ambient atmosphere, they will be used as building blocks for novel nano-structure-controlled materials.