EFFECT OF CARBON SUBSTITUTION ON THE MAGNETIC-PROPERTIES AND CRYSTALLINE PHASES OF MELT-SPUN ND4FE77.5B18.5 ALLOYS

The magnetic properties and crystallized phases of melt-spun Nd4Fe77.5B18.5-xCx (x=0, 4, 6, 8, and 10) alloys have been investigated by means of zero-field spin-echo nuclear magnetic resonance (NMR), x-ray diffraction, and magnetization measurements. The results show that the Curie temperatures of amorphous alloys have a small dependence on carbon concentration, the saturation magnetization of amorphous alloys and the average magnetic moment per Fe atom are found to have a small increase, as x increases from x=0 to x=10, and, the crystallization temperatures of amorphous alloys decrease with increasing carbon concentration. The amorphous alloys are magnetically soft; their coercive fields are less than 10 Oe. When the ribbons are annealed over the crystallization temperature, the coercivity increases rapidly and reaches a maximum value at the annealing temperature of about 670°C, then decreases monotonically. Previous studies demonstrated that Nd4Fe77.5B18.5 alloys annealed at 670°C for a short time consisted only of body-centered-tetragonal Fe3B (bct Fe3B) and a few percent of α-Fe. After a short anneal at 670°C, the coercivity of crystallized alloys decreases with increasing carbon content, with a simultaneous development of an orthorhombic Fe3B(o-Fe3B) phase. Furthermore, the NMR study demonstrates that o-Fe3B has softer magnetic properties than bct Fe3B. It can be concluded that the addition of carbon in Nd4Fe77.5B18.5 alloy favors the transformation from bct Fe3B to o-Fe3(B,C) and the decrease of coercivity is due to the presence of o-Fe3(B,C). © 1995 The American Physical Society.