Spin-Glass-Like Characteristics Of Extremely Small Gamma-Fe2o3 Nanoparticles

Magnetic measurements on small gamma-Fe2O3 particles (diameter D similar to 3nm) have been carried out. Features in the zero-field-cooled and field-cooled magnetization data and the high-field irreversibility in the low-temperature hysteresis curve are found to be consistent with a collective thermal blocking process. The dynamical properties, studied by ac magnetic susceptibility measurements, suggest the occurrence of a spin-glass like transition with a critical exponent zv = 8.0 +/- 0.8. This finding is also supported by the H-2/3-dependence of the temperature transition (T-g) which is consistent with the Almeida-Thouless critical line (delta T-g similar to H-2/3) of canonical spin glasses.