Disordered Magnetism at the Grain Boundary of Pure Nanocrystalline Iron

The low-temperature magnetic behavior of ball-milled nanocrystalline Fe is reported. The results of dc and ac susceptibility, remanence, and magnetic relaxation measurements indicate a transition from a high-temperature ferromagnetic state to a low-temperature disordered regime, where a collective freezing of the crystallites magnetic moments occurs. It is proposed that the behavior is determined by the presence of the structurally disordered grain boundaries, showing spin-glass-like properties.