The role of dipolar interactions among Ni nanoparticles (NPs) embedded in an amorphous ${\text{SiO}}_2/\text{C}$ matrix with different concentrations has been studied performing ac magnetic susceptibility ${\chi }_{\text{ac}}$ measurements. For very diluted samples, with Ni concentrations $<4\text{wt}\%$ Ni or very weak dipolar interactions, the data are well described by the Néel-Arrhenius law. Increasing Ni concentration to values up to $12.8\text{wt}\%$ Ni results in changes in the Néel-Arrhenius behavior, the dipolar interactions become important, and need to be considered to describe the magnetic response of the NPs system. We have found no evidence of a spin-glasslike behavior in our Ni NP systems even when dipolar interactions are clearly present.

• Received 6 July 2009

DOI:https://doi.org/10.1103/PhysRevB.80.184428