DC and AC magnetization and small-angle neutron scattering studies of strongly interacting particle systems

Abstract MnZn-ferrite particles were randomly dispersed in polymer matrix in which the magnetic anisotropy axes in the particles are randomly oriented. DC and AC magnetization and small-angle neutron scattering measurements have been made on the samples. The DC and AC susceptibilities showed spin-glass-like maxima at temperatures that depend on the interparticle interaction. The thermal evolution of remanence I r and coercivity H c was also considerably dependent on the interparticle interaction, i.e., the temperature at which I r and H c tend to zero increased with increasing the interparticle interaction energy. This suggests that a magnetic correlation occurs through the interparticle interaction in the present sample. The temperature dependence of imaginary part of the AC susceptibility χ ″ showed a singular cusp at a low temperature which is insensitive to the interparticle interaction. This singularity in χ ″ could reflect a blocking phenomena which is attributed to the intraparticle anisotropy. The small-angle magnetic neutron scattering line shape over a temperature range of 6⩽ T ⩽260 K could be represented by a function of Lorentzian plus squared Lorentzian which is appropriate for a random anisotropy field system. The data did not show a divergence in the magnetic correlation length, but suggested the formation of a local ferromagnetic cluster composed of the magnetic moments of the adjacent particles below 260 K. The correlation length increases with decreasing temperature. Around 40 K, it shows a maximum and starts to decrease with decreasing temperature. This decrease in the correlation length with decreasing temperature could arise from the random field effect which could originate from the intraparticle anisotropy.