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Magnetic hysteresis and magnetic Barkhausen emission (MBE) parameters have been studied for as-received and annealed Fe72Nb4.5Cu1Si13.5B9 alloys. The coercivity rapidly decreased at the initial stage of annealing, in contrast to the slow change of root-mean-square voltage of Barkhausen emissions. The amplitude of the Barkhausen emission signal reduced almost to the background noise level at an intermediate annealing temperature, at which the material exhibited superior soft magnetic properties. Pulse height distribution of the MBE signal showed the existence of a large number of small amplitude pulses at the intermediate range of annealing, an indication that the magnetization process of the system is dominated by the rotation of the magnetization vector within a small volume of nanocrystalline particles. We explain the results by a random anisotropy model, assuming the exchange coupling between the Fe80Si20 nanograins of higher magnetic moment takes place through the magnetically weaker amorphous matrix.
Date of Publication: Nov 2002