Nd2Co7−xFexB3 alloys have been synthesized and studied at temperatures from 4 to 1100 K at fields up to 90 kOe. The structure and magnetic properties vary significantly with changing Fe content. The main phase is observed to be of hexagonal symmetry for x<3. For x>4 it is multiphase, the major phase having tetragonal symmetry. The Tc increases from 330 to 885 K when x varies from 0 to 3, then decreases from 885 to 577 K when x increases from 3 to 7. The saturation magnetization is 8μB/fu at 4.2 K, for Nd2Co7B3; it increases with increasing Fe content. The alloys exhibit a conical (0<x<3) and an axial (x>4) magnetocrystalline anisotropy at 295 K. They all exhibit conical magnetic anisotropy at 77 K.

In this article, we report types of magnetic domain patterns caused by either dipolar coupling or exchange coupling inside a heat-treated boron-rich NdFeB melt-spun ribbon. The average grain size of the sample was about 38 nm. Single particle domains were commonly observed in Fresnel images all through the specimen, suggesting little exchange coupling among the grains in these regions. Snake-shaped long interactive domains consisting of chains of grains were found in many Foucault images at the regions where exchange coupling is weak. These domains are caused by dipolar coupling along the chains. Wider domains consisting of many grains were also observed by Fresnel images, although they were much less common than the single particle domains. The grains inside a wider domain are believed to be exchange coupled with each other. The magnetic properties of such boron-rich NdFeB composites are influenced more by the dipolar coupling than by exchange coupling between the nanocrystalline grains.