The phase composition of crystallized NdxFe81.5minus;xB18.5(x=3, 4, 4.5, 6, 12, and 15) alloys annealed under optimal condition are investigated by means of zerohyphen;field spinhyphen;echo nuclear magnetic resonance (NMR) and Mouml;ssbauer effect (ME), together with xhyphen;ray diffraction (XRD). It is found that the phase composition depends on the Nd concentration. The samples with 12ndash;16 at.thinsp;percnt;hyphen;Nd contain Nd2Fe14B magnetically hard phase and Nd1.1Fe4B4paramagnetic phase. Their large coercive fields are due to the very fine size of Nd2Fe14B crystallite below the critical size of single domain particles, and some minor phases precipitated at grain boundaries, which have a pinning domain wall effect. The samples with a lower Nd concentration (x=3ndash;6 at.thinsp;percnt;) consist of bodyhyphen;centeredhyphen;tetragonal (bct)hyphen;Fe3B and a small amount of agr;hyphen;Fe, and no Nd2Fe14B and Nd1.1Fe4B4. Furthermore, the NMR results show that the spectra corresponding to bcthyphen;Fe3B in the samples annealed at 670thinsp;deg;C distort and broaden more seriously than that of pure bcthyphen;Fe3B in the Nd4Fe77.5B18.5alloy annealed at 839thinsp;deg;C, and the difference of their spinhyphen;lattice and spinhyphen;spin relaxation time is very large, implying that B atoms have at a different nearesthyphen;neighbor environment. Thus, it is reasonable to assume that Nd atoms enter into bcthyphen;Fe3B and that such a compound has a large coercive field.
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