Nanostructure and magnetic properties of CoNi-alloy-based nanoparticles dispersed in a silica matrix

A comparative study of the magnetic behavior of FCC alloy CoNi (1 : 1) nanoparticles, embedded in a silica matrix and prepared by the ion implantation and sol-gel techniques, is presented. The blocking temperature is related to the size distribution, and, at least for the ion-implanted samples, only an enhanced effective anisotropy explains the experimental results. The hysteretic behavior is explained in terms of the temperature dependence of the anisotropy and of the particle volume fraction that determines the dipolar interactions.