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

A comparative study of the magnetic properties of Co and Ni based alloy nan oparticles (Ni-Co, Ni-Cu and Co-Cu) formed in a silica matrix by ion implan tation is presented. Different ion doses and implantation sequences were re alized in order to obtain different nanostructures. The structural and magn etic properties observed for the Cu50Ni50 nanoparticles are similar to thos e of the Cu60Ni40 bulk alloy. The crystal structure of CoxNi1-x (0 less tha n or equal to x less than or equal to 1) nanoparticles is similar to that o f the corresponding bulk alloy. The magnetic properties depend on the ion-i mplanted dose and on the alloy composition. The samples prepared by implant ing a 15 x 10(16) ions/cm(2) total dose contain nanoparticles, which are su perparamagnetic at room temperature and their magnetic behavior is influenc ed by dipolar interparticle interactions. The magnetization of the CoNi sam ples at high magnetic field is larger than that of the corresponding bulk a lloy and follows the same composition dependence of that quantity measured in the alloy. (C) 2001 Elsevier Science B.V. All rights reserved.