Magnetic coupling in boron-rich NeFeB nanocomposites

Abstract

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.

Microstructure and magnetic properties of NdxFe85−xTi4B10.5C0.5 (x=7.8, 8.2, 8.6, 9.0, and 9.4) nanocomposite alloys with Ti and C additions

“…Recently, nanocomposite magnets with a composition of about 9-10 at% neodymium and 10-14 at% boron receive much interest due to the good balance of coercivity and remanence [5][6][7][8]. In this alloy composition, the addition of Ti is found to be particularly effective in suppressing the formation of a-Fe and promoting the formation of Nd 2 Fe 14 B; small C addition provides additional grain refinement, which leads to the increase of coercivity without sacrificing much remanence [9][10][11].…”