Mössbauer Spectroscopy and X-Ray Diffraction Studies of the Phase Composition of Crystallized Nd_(x)Fe_(81.5-x)B_(18.5) Alloys with 7 ≤ x ≤15

The phase composition of melt-spun Nd-Fe-B with intermediate and high Nd concentrations has been studied by Mössbauer effect.Based on the knowledge of the ^(57)Fe hyperfine parameters for Nd_(2)Fe_(14)B,Nd_(2)Fe_(23)B_(3),and Nd_(1.1)Fe_(4)B_(4),the phases produced during annealing Nd-Fe-B amorphous alloys can be identified.It is found that the Nd_(x)Fe_(81.5-x)B_(18.5) samples with 7≤x≤9 contain the Nd_(2)Fe_(23)B_(3) metastable phase and the Nd1.1Fe4B4 paramagnetic phase.The body-centered-cubic structure of Nd_(2)Fe_(23)B_(3) cannot generate the hard magnetic properties.The samples with 12≤x≤15 consist of the Nd_(2)Fe_(14)B hard magnetic phase and the Nd1.1Fe4B4 paramagnetic phase.The large coercivity for the high Nd content Nd-Fe-B originates from the very fine size of Nd_(2)Fe_(14)B grains below the particle size of the single domain,which may contribute to a pinning effect of domain wall.