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  • 1990-1994  (2)
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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Until now, the origin of hard magnetic properties of rapidly quenched Nd-Fe-B alloys with lower Nd concentration is not clear. In this paper, the phase compositions of rapidly quenched Nd4Fe77.5B18.5 alloys annealed under different conditions have been studied by using zero-field spin-echo nuclear magnetic resonance (NMR) and Mössbauer effect (ME) techniques. It is found that there exists a certain amount of Nd2Fe14B phase in the samples annealed at 960 °C and ingot alloy, which have poor hard magnetic properties; while, the sample annealed under optimal condition consists only of bct-Fe3B as the main phase and a small amount of a-Fe. However, the ME result indicates that about 5 at. % Fe atoms in FeIII (8 g) site of bct-Fe3B have been replaced by Nd atoms; the NMR result demonstrates that 11B NMR spectrum is the characteristic peak of bct-Fe3B, but it broadens asymmetrically to the high frequency side, which is due to the bct-Fe3B influenced by Nd atoms. The amplitude of radio frequency (rf) excitation field required to get the maximum 11B spin-echo signal from bct-Fe3B in the sample annealed at 839 °C is only about one third as much as that required to excite the 11B in the bct-Fe3B influenced by Nd atoms in the sample annealed at 670 °C for a short time, which implies the latter has a larger coercivity field than the former. It is concluded that the origin of hard magnetic properties of Nd4Fe77.5B18.5 alloy is not related to the 2:14:1 phase, but to the change of bct-Fe3B itself.
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Fe–B amorphous alloys powders with high boron concentration can be prepared by borohydride reduction (BHR). By adjusting technological factors, the Fe100−xBx amorphous powders with compositions ranging from x=17 to 40 can be easily obtained, but it is difficult to make the amorphous ribbons with such a high B concentration by using rapidly quenched technique, which can usually obtain the amorphous ribbons with the compositions ranging from x=12 to 25. Up to now, there are different points of view about if the short range order (SRO) in the Fe–B amorphous powders prepared by the BHR around room temperature is the same with that in the amorphous ribbons made by rapidly quenched and vapor depositing techniques. In this paper, the SRO in Fe100−xBx amorphous powders with various boron concentration prepared by the BHR have been studied by the zero field spin echo nuclear magnetic resonance (NMR) technique. It was shown that the types of SRO in these samples vary with the B concentration. There exist Fe3B- and Fe2B-like SRO and a small amount of α-Fe in the samples with lower B concentration, while there are Fe3B- and FeB-like SRO in the alloys with higher B concentration. Fe3B-like SRO, however, only exists in the amorphous ribbons obtained by rapidly quenched method. It can be concluded that there are different types of SRO in the amorphous alloys prepared by different methods. This conclusion can explain the reason why the average hyperfine field at Fe sites deceases with the B concentration increasing.
    Type of Medium: Electronic Resource
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