Magnetic hardening of Fe-Nb-B-Tb type of bulk nanocrystalline alloys

Phase structure and magnetic properties of the (Fe80Nb6B14)1−xTbx family of bulk nanocrystalline alloys were thoroughly examined. The samples were obtained by suction casting technique for x = 0.1, 0.11 and 0.12, using three different diameters of the casting mould: d = 0.5, 1 and 2 mm. 57Fe Mössbauer spectrometry showed that the studied samples contain about 65% Tb2Fe14B hard magnetic phase and TbFe2/α-Fe soft phases. At 300 K, sample with 12% of Tb with the lowest diameter (d = 0.5 mm) exhibited the best hard magnetic properties, i.e. coercive field μ0HC = 3.36 T and energy product |BH|max = 121 kJ/m3. Moreover, according to Tb content and sample diameter values, an asymmetric shape of magnetic hysteresis was observed. The obtained hard magnetic properties resulted from the magnetic interactions between the hard and soft phases forming the complex micro- (nano-) structure produced by the applied fabrication technique.