Nickel nano-particles in silica gel monoliths: control of the size and magnetic properties

Monolithic samples containing I and 5 mol% of nickel(II) have been prepared . After thermal treatment Ni(II) is reduced to metallic Ni particles, the s ize of the particles and the inter-particles distances have been controlled by the nickel content and treatment temperatures. The magnetic susceptibil ity exhibits a maximum (corresponding to blocking temperature T-B) below th e bifurcation point in the ZFC/FC data, consistent with the description of super-paramagnetism. The maximum shifts toward higher temperature with incr easing Ni concentration. In the super-paramagnetic state (T > T-B), the low field susceptibility does not follow a Curie-Weiss law. These phenomena co uld result to inter-particles dipolar interactions. (C) 2001 Elsevier Scien ce BN. All tights reserved.