MAGNETIC-BEHAVIOR OF GAMMA-FE2O3 NANOPARTICLES BY MOSSBAUER-SPECTROSCOPY AND MAGNETIC MEASUREMENTS

gamma-Fe2O3 nanoparticles with varying state of dispersion in a polymer have been investigated by Mossbauer spectroscopy, static magnetic measurements at low applied field, and alternative susceptibility measurements over a large range of frequencies (2 x 10(-2)-10(4) Hz). The dynamical behaviour was characterized through the variation of the blocking temperature with the characteristic time of the measurement. The Mossbauer blocking temperature was determined according to a procedure described. For quasi-isolated particles an Arrhenius law is demonstrated. Effects of interparticle interactions in concentrated and aggregated systems are satisfactorily explained by the previous model. Dependence of the superparamagnetic susceptibility on the experimental conditions interpreted using the Lorentz or Onsager fields is mentioned.