  The linear and cubic dynamic susceptibilities of solid dispersions of
nano-sized maghemite particles have been measured for three samples with a
volume concentration of magnetic particles ranging from 0.3 % to 17 %, in order
to study the effect of dipole-dipole interactions. Significant differences
between the dynamic response of the three samples are observed. The dynamic
susceptibilities of the most dilute sample compare reasonably well with an
existing theory for the linear and cubic dynamic susceptibilities of an
assembly of noninteracting, uniaxial magnetic particles. The nonlinear dynamic
response of the most concentrated sample exhibits at low temperatures some of
the features observed in a Ag(11 at.% Mn) spin glass.
