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 crystall ized R(x)Nd(4-x)Fe(77.5)B(18.5) (R = Y, Pr, Gd or Dy; 0 less than or e qual to x less than or equal to 4) alloys have been investigated by me ans of magnetization measurements, zero-field spin-echo nuclear magnet ic resonance (NMR) and the Mossbauer effect (ME). It is found that the Curie temperatures of amorphous alloys change slightly on the additio n of R, but the coercive fields of crystallized alloys decrease monoto nically 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 a nd 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 o f Fe3B with a body-centred tetragonal (BCT) structure and a small amou nt of alpha-Fe. Furthermore, the NMR results indicate that the B-11 hy perfine fields of sn Fe3B increase linearly from 25.3 kOe (34.7 MHz) t o 26.3 kOe (36.0 MHz) on the addition of Dy or Gd, but that of alpha-F e does not change with increasing R concentration; the Mossbauer spect ra show that the relative intensity of the subspectrum corresponding t o 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 t o assume that R atoms enter into BCT Fe3B.