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

Monolithic samples containing 1 and 5 mol% of nickel(II) have been prepared. After thermal treatment Ni(II) is reduced to metallic Ni particles, the size of the particles and the inter-particles distances have been controlled by the nickel content and treatment temperatures. The magnetic susceptibility exhibits a maximum (corresponding to blocking temperature TB) below the bifurcation point in the ZFC/FC data, consistent with the description of super-paramagnetism. The maximum shifts toward higher temperature with increasing Ni concentration. In the super-paramagnetic state (T>TB), the low field susceptibility does not follow a Curie–Weiss law. These phenomena could result to inter-particles dipolar interactions.