Effects of ion irradiation on cobalt nanocomposite

The effects of ion irradiation of 3-dimensional arrays of Co nanoparticles were investigated. Arrays were obtained by electron beam deposition of 15 Co/SiO₂ bilayers 0.5 and 20 nm thick, respectively. The Co layers consist of Co nanoparticles 3.2 nm in diameter with a standard deviation of 16%. Irradiation was carried out using combinations of 150 kV Ar²⁺ and 90 kV Ar⁺ ion bombardments with a Ar⁺:Ar²⁺ fluence ratio of 1:4. The effects of ion irradiation were followed by Rutherford backscattering, measurements of hysteresis loops at 5 K and of temperature-dependent field-cooled (FC) and zero-field-cooled (ZFC) measurements of the magnetic susceptibility. A decrease of the peak temperature in the ZFC curve for displacements per atom (DPA) up to 1.1 was observed. Irradiation also induces progressively lower coercivity values. The Co particles showed a remarkable high resistance to ion irradiation, surviving damage up to 33 DPA.