Superparamagnetism in cobalt nanoparticles synthesized by ion implantation in thin polyimide

Thin polyimide layers with cobalt nanoparticles were synthesized by high-fluence ion implantation at the dose ranging 2,5×1016 - 7,5×1016 cm-2 and ion current density j=4,0 mA/cm2 with energy 40 keV. At fluence lower than 5×1016 cm-2 cobalt clusters show superparamagnetic behaviour being Langevin equation up to blocking temperature. At higher fluence magnetic interaction appears because of growing clusters size and conductivity increasing due to carbonization of near-surface layer. Assuming spherical shape of the clusters an estimation of mean clusters size are made for a, b, and e-cobalt crystalline modifications which rang in the interval 1,7 - 4,5 nm. (authors)