Abstract
By analytical electron microscopy and Lorentz microscopy, microstructures and magnetic domain structures of Nd–Fe–B nanocomposite magnets prepared by the melt-spun technique which consists of a mixture of hard and soft magnetic phases were investigated. By energy dispersive X-ray spectroscopy elemental mapping for the neodymium element, hard (Nd2Fe14B) magnetic grains were distinguished from soft (Fe3B or α-Fe) magnetic grains. The Fe3B grains could be further distinguished from the α-Fe grains by investigating the boron K-edge in electron energy-loss spectroscopy, despite the strong background in the spectra. From bright-field electron microscopy coupled with energy dispersive X-ray spectroscopy elemental mapping, the grain size distribution 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 evaluated to be about 32 nm and 35 nm, respectively. Through Lorentz microscopy study on the Nd4.5Fe77B18.5 magnet annealed at 973 K, the size of the magnetic 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.
