THE EFFECT OF GD SUBSTITUTION ON THE MAGNETIC-PROPERTIES AND HYPERFINE FIELDS OF MELT-SPUN ND4FE77.5B18.5 ALLOYS

The hyperfine fields (HFS) and magnetic properties of amorphous and crystallized Gd(x)Nd4-xFe77.5B18.5 (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 Mossbauer effect (ME). For comparison, the x-ray diffraction (XRD) pattern of Nd4Fe77.5B18.5 annealed at 670-degrees-C for a short time is also presented. It is found that the Curie temperatures of amorphous alloys increase slightly on addition of Gd, but the coercive fields of crystallized alloys decrease monotonically with increasing x. NMR, ME and XRD indicate that these samples consist of Fe3B with a body-centred tetragonal structure (BCT Fe3B) and a small amount of alpha-Fe, with no Nd2Fe14B and Nd1.1Fe4B4 phases. Furthermore, the NMR results indicate that the B-11 HFS of BCT Fe3B increase linearly from 25.3 kOe (34.7 MHz) for x = 0 to 26.3 kOe (36.0 MHz) for x = 4, but that of alpha-Fe does not change with increasing Gd concentration; the Mossbauer spectra (MSS) 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 the R atoms enter into the BCT Fe3B.