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. 
S. H. Masunaga, R. F. Jardim, R. S. Freitas and J. Rivas
cond-mat.str-el cond-mat.mes-hall