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

gamma-Fe2O3 nanoparticles with varying state of dispersion in a polyme r have been investigated by Mossbauer spectroscopy, static magnetic me asurements at low applied field, and alternative susceptibility measur ements over a large range of frequencies (2 x 10(-2)-10(4) Hz). The dy namical behaviour was characterized through the variation of the block ing temperature with the characteristic time of the measurement. The M ossbauer blocking temperature was determined according to a procedure described. For quasi-isolated particles an Arrhenius law is demonstrat ed. Effects of interparticle interactions in concentrated and aggregat ed systems are satisfactorily explained by the previous model. Depende nce of the superparamagnetic susceptibility on the experimental condit ions interpreted using the Lorentz or Onsager fields is mentioned.