Formation of ferromagnetic Ni/SiO2 nanospheres

Dispersed SiO2 nanospheres have been nickel-plated using an electroless-plating solution. Magnetic resonance (MR) experiments have been performed on these samples. The MR signals demonstrate the presence of Ni+2 and Ni+3 paramagnetic centers, which are most easily seen below 40 K, and ferromagnetic metallic Ni, which can be readily seen above 40 K. The MR results also indicate only the presence of paramagnetic Ni+3 in a dried sample of the Ni-plating solution that does not contain any SiO2 nanospheres. These results suggest that an interfacial reaction at the surface of the SiO2 nanospheres leads to the formation of ferromagnetic Ni, which deposits onto the spheres and forms a Ni/SiO2 nanosphere composite. (C) 2002 Elsevier Science B.V. All rights reserved.