Magnetic coupling in boron-rich NeFeB nanocomposites

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. © 1999 American Institute of Physics. @S0021-8979~99!47608-X#