Magnetism of AuFe nanoparticles

The time-dependent magnetization of Au_81.7Fe_18.3 nanoparticles was investigated under field-cooled and zero-field-cooled conditions. In the Au_81.7Fe_18.3 nanoparticles a spin-glass-like phase appears below 10 K; the field-cooled and zero-field-cooled magnetizations reach the upper bound value within about 1500 s. This is the first observation of the entire process of evolution from the non-equilibrium spin-glass-like state to the equilibrium state. This peculiar relaxation process in the Au_81.7Fe_18.3 nanoparticles may be interpreted by the decrease in characteristic relaxation time owing to simplification of the multi-valley structure of the free energy and/or a lowered energy barrier as a surface effect.