EVIDENCE OF SPIN DISORDER AT THE SURFACE-CORE INTERFACE OF OXYGEN PASSIVATED FE NANOPARTICLES

Hysteresis, thermal dependence of magnetization, and coercivity of oxi de coated ultrafine Fe particles prepared by inert gas condensation an d oxygen passivation have been studied in the 5-300 K range. The resul ts are found to be consistent with a spin-glasslike state of the oxide layer inducing, through exchange interaction with the ferromagnetic c ore, a shift of the field cooled hysteresis loops at temperatures belo w the freezing at approximately 50 K. (C) 1998 American Institute of P hysics. [S0021-8979(98)07315-0].