Grain-boundary structure in nanocrystalline ball-milled FeRh

Starting from four different FeRh compositions, a nanocrystalline fee phase has been obtained, for each case, through mechanical alloying by ball-milling. At low temperatures, some characteristic behaviors typical of the spin-glass or superparamagnetic state have been observed in all the compositions: a maximum of AC and ZFC: susceptibility at a temperature T-max weakly dependent on the frequency and oil the applied field, which increases with the grain size, and a broad distribution of hyper-tine fields in the Mossbauer spectra at T<T-max. Actually, all the results seem to indicate that the observed behavior is intrinsic to the nanocrystalline nature of fee FeRh. The shifted hysteresis loop observed after field cooling as well as the remarkable irreversibility in high fields indicate that T-max corresponds to the freezing temperature of the strongly deformed grain boundaries, which behave as spin-glass-like phase.