MAGNETIC-PROPERTIES OF NI NANOPARTICLES DISPERSED IN SILICA PREPARED BY HIGH-ENERGY BALL-MILLING

We analyze the magnetic properties of mechanically ground nanosized Wi particles dispersed in a SiO2 matrix. Our magnetic characterization o f the as-milled samples show the occurrence of two blocking processes and that of non-monotonic milling time evolutions of the magnetic-orde r temperature, the high-field magnetization and the saturation Coerciv ity. The measured coercivities exhibit giant values and a uniaxial-typ e temperature dependence. Thermal treatment carried out in the as-prep ared samples result in a remarkable coercivity reduction and in an inc rease of the high-field magnetization. We conclude, on the basis of th e consideration of a core (pure Wi) and shell (Ni-Si inhomogeneous all oy) particle structure, that the magnetoelastic anisotropy plays the d ominant role in determining the magnetic properties of our particles.