Analysis of microstructures and magnetic domain structures in Nd-Fe-B nanocomposite magnets by analytical electron microscopy and Lorentz microscopy

By analytical electron microscopy and Lorentz microscopy, microstructures a nd magnetic domain structures of Nd-Fe-B nanocomposite magnets prepared by the melt-spun technique which consists of a mixture of hard and soft magnet ic phases were investigated. By energy dispersive X-ray spectroscopy elemen tal mapping for the neodymium element, hard (Nd2Fe14B) magnetic grains were distinguished from soft (Fe3B or alpha -Fe) magnetic grains. The Fe3B grai ns could be further distinguished from the a-Fe grains by investigating the boron K-edge in electron energy-loss spectroscopy, despite the strong back ground in the spectra. From bright-field electron microscopy coupled with e nergy dispersive X-ray spectroscopy elemental mapping, the grain size distr ibution of constituent phases in a Nd4.5Fe77B18.5 magnet annealed at 973 K was evaluated. An average grain size of Fe3B and Nd2Fe14B grains was evalua ted to be about 32 nm and 35 run, respectively. Through Lorentz microscopy study on the Nd4.5Fe77B18.5 magnet annealed at 973 K, the size of the magne tic domain formed through the exchange interaction was found to be 100-150 nm being much larger than the grain sizes of Fe3B and Nd2Fe14B phases.