Magnetism and hyperfine fields in melt-spun R-Fe-B alloys with a low R concentration (R≡Y, Pr, Nd, Gd or Dy)

The hyperfine fields and magnetic properties of amorphous and crystallized R(x)Nd(4-x)Fe(77.5)B(18.5) (R = Y, Pr, Gd or Dy; 0 less than or equal to x less than or equal to 4) alloys have been investigated by means of magnetization measurements, zero-field spin-echo nuclear magnetic resonance (NMR) and the Mossbauer effect (ME). It is found that the Curie temperatures of amorphous alloys change slightly on the addition of R, but the coercive fields of crystallized alloys decrease monotonically with increasing x for R = Y, Pr and Gd. A small addition of Dy increases the coercivity; full substitution of Nd by Dy leads to low coercivity owing to the formation of the magnetically soft Dy3Fe62B14. NMR, ME and x-ray diffraction indicate that the samples with R = Pr and Gd for 0 less than or equal to x less than or equal to 4 and R = Y and Dy for 0 less than or equal to x less than or equal to 2 consist of Fe3B with a body-centred tetragonal (BCT) structure and a small amount of alpha-Fe. Furthermore, the NMR results indicate that the B-11 hyperfine fields of sn Fe3B increase linearly from 25.3 kOe (34.7 MHz) to 26.3 kOe (36.0 MHz) on the addition of Dy or Gd, but that of alpha-Fe does not change with increasing R concentration; the Mossbauer spectra show that the relative intensity of the subspectrum corresponding to Fe-57 at Fe-III(8g) sites in BCT Fe3B is about 5% weaker than those of the other two, implying that about 5 at.% Fe atoms in this site are substituted by other atoms. According to this, it may be reasonable to assume that R atoms enter into BCT Fe3B.