  We report the magnetic properties of magnetic nano-composite, consisting of
different quantity of NiFe2O4 nanoparticles in polymer matrix. The
nanoparticles exhibited a typical magnetization blocking, which is sensitive on
the variation of magnetic field, mode of zero field cooled/field cooled
experiments and particle quantity in the matrix. The samples with lower
particle quantity showed an upturn of magnetization down to 5 K, whereas the
blocking of magnetization dominates at lower temperatures as the particle
quantity increases in the polymer. We examine such magnetic behaviour in terms
of the competitive magnetic ordering between core and surface spins of
nanoparticles, taking into account the effect of inter-particle (dipole-dipole)
interactions on nanoparticle magnetic dynamics.
