Magnetic interactions in nanocrystalline FeRh alloys studied by in field M?ssbauer spectroscopy

The results of a M?ssbauer spectroscopy study of the fcc ball-milled FeRh alloy in the temperature range 4.2-90 K and in applied fields up to 7 T corroborated with an earlier magnetic investigation were interpreted starting from a system of nanograins with bulk spin-glass properties and a small uncompensated average grain moment of 103 mu B exchange coupled via the spin glass disorder in the region of the grain boundaries. Besides the thermal fluctuations of the exchange coupled atomic spins in the bulk, those of the uncompensated magnetic moments of the nanograins give rise to a more rapid decrease of the average hyperfine field with increasing temperature and to its collapse at temperatures between 80 and 90 K, at which the nanograins behave as free paramagnetic particles.