Boundary spin disorder in nanocrystalline FeRh alloys

The magnetic properties of the ball-milled nanocrystalline fee phase of FeRh alloys are reported and discussed. The observed features (maximum of ac and zero-field cooling susceptibility at a temperature T-max weakly dependent on the frequency and on the applied field) suggest a progressive blocking of moments of nanograins with decreasing temperature, followed by their collective freezing in random directions at T-max. The shifted hysteresis loop observed after field cooling as well as the remarkable irreversibility in high fields indicates that T-max corresponds to the freezing temperature of the strongly deformed grain boundaries, which behave as a spin-glass-like phase.