  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.
