Increase in the magnitude of the energy barrier distribution in Ni nanoparticles due to dipolar interactions

The energy barrier distribution Eb of five samples with different concentrations x of Ni nanoparticles using scaling plots from ac magnetic susceptibility data has been determined. The scaling of the imaginary part of the susceptibility Chi(nu, T) vs. Tln(t/tau_0) remains valid for all samples, which display Ni nanoparticles with similar shape and size. The mean value <E_b> increases appreciably with increasing x, or more appropriately with increasing dipolar interactions between Ni nanoparticles. We argue that such an increase in <Eb> constitutes a powerful tool for quality control in magnetic recording media technology where the dipolar interaction plays an important role.

Role of dipolar interactions in a system of Ni nanoparticles studied by magnetic susceptibility measurements

The role of dipolar interactions among Ni nanoparticles (NP) embedded in an amorphous SiO2/C matrix with different concentrations has been studied performing ac magnetic susceptibility Chi_ac measurements. For very diluted samples, with Ni concentrations < 4 wt % Ni or very weak dipolar interactions, the data are well described by the Neel-Arrhenius law. Increasing Ni concentration to values up to 12.8 wt % Ni results in changes in the Neel-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.