Phase structure and magnetic properties of Fe–Nb–B–Tb type of bulk nanocrystalline alloys

► Magnetic properties of (Fe80Nb6B14)1−xTbx bulk nanocrystalline alloys were tested. ► Formation of Tb2Fe14B and TbFe2/α–Fe nanocrystalline phases was detected. ► Alloys with 0.8⩽x⩽0.12 are magnetically hard (for x=0.1 Hc=1.46T). ► Maximum of energy product |BH|max=94.9kJ/m3 was observed for x=0.12. Phase structure and magnetic properties of the (Fe80Nb6B14)1-xTbx family of bulk nanocrystalline alloys obtained by suction casting technique were carefully examined. It was shown (Mössbauer spectra, XRD spectra) that the examined samples contain magnetically hard Tb2Fe14B and other TbFe2/α–Fe soft phases - the higher Tb content the higher contribution of TbFe2. It was also shown that in the examined alloy family there is an optimal Tb content (estimated as 11%). Around this point one can observe a maximum of coercive field (for 10% Hc=1.46T at T=300K), maximum of relative remanence (for 12% MR/MS=0.82) and maximum of energy product (for 12% |BH|max=94.9kJ/m3). It seems that the observed effect can be explained via blocking of magnetic moments effects caused by a local magnetocrystalline anisotropy as well as structural disorder introduced by the applied sample fabrication technique.