Magnetic properties of Co and Ni alloy nanoparticles dispersed in a silica matrix

A comparative study of the magnetic properties of Co and Ni based alloy nanoparticles (Ni-Co, Ni-Cu and Co-Cu) formed in a silica matrix by ion implantation is presented. Different ion doses and implantation sequences were realized in order to obtain different nanostructures. The structural and magnetic properties observed for the Cu(50)Ni(50) nanoparticles are similar to those of the Cu(60)Ni(40) bulk alloy. The crystal structure of Co(x)Ni(1-x) (0 less than or equal to x less than or equal to 1) nanoparticles is similar to that of the corresponding bulk alloy. The magnetic properties depend on the ion-implanted dose and on the alloy composition. The samples prepared by implanting a 15 x 10(16) ions/cm(2) total dose contain nanoparticles, which are superparamagnetic at room temperature and their magnetic behavior is influenced by dipolar interparticle interactions. The magnetization of the CoNi samples at high magnetic field is larger than that of the corresponding bulk alloy and follows the same composition dependence of that quantity measured in the alloy.