Phase Stability of $(Fe_{80}Nb_{6}B_{14})_{0.9}Tb_{0.1}$ Bulk Nanocrystalline Magnet

The paper refers to phase stability of the $(Fe_{80}Nb_{6}B_{14})_{0.9}Tb_{0.1}$ bulk nanocrystalline alloys prepared using the vacuum suction casting technique. The samples were in the form of rods with diameters d=2, 1.5, 1 and 0.5 mm. Heating up to 900 K reveals structural changes that occur at temperatures above 680 K (DSC and M(T) measurements). The phase analysis, using Mössbauer spectra, indicates the decrease of $Tb_{2}Fe_{14}B$ and increase of Fe content in the samples after the heat treatment. The most stable is the alloy with d=1 mm, where the formation of α-Fe phase was not observed. The decrease of d causes significant hardening i.e. coercive field increases from 0.57 T to 2.66 T for d=2 mm and d=0.5 mm, respectively.