Electron holography on remanent magnetization distribution of melt-spun Nd-Fe-B magnets

Microstructures and magnetic domain structures of melt-spun Nd-Fe-B permanent magnets were investigated in detail by analytical electron microscopy and electron holography. While the crystal orientation of matrix Nd ₂Fe₁₄B grains was analyzed by nanobeam electron diffraction, precipitates of a few tens of nanometers at grain boundaries were identified to be α-Fe by energy-dispersive X-ray spectroscopy. The detailed magnetization distribution in Nd₂Fe₁₄B grains and at their boundaries was visualized by electron holography. Ex situ experimentation with an electromagnet revealed that the domain walls in the demagnetized state and remanent states were pinned at grain boundaries, and Fe precipitates at the grain boundary were situated at the center of the closure domain.