Magnetic properties of permanent magnets are sensitive to their microstructure. In particular, for a class of Nd(Pr)-Fe-B magnets very different coercivity and energy products may be obtained by different processing techniques. In this work we report on the preliminary results of magnetic domains (MD) structure and grain boundaries (GB) analysis of such hot-deformed Nd(Pr)-Fe-B magnets. To reveal the fine details of MD and GB interaction the experiments were carried out by the combined use of Magnetic Foucault-Fresnel Imaging and High Resolution Microscopy.
The magnets used in this study had a nominal composition Nd13.75Fe80.25B6 (I) and Pr13.75Fe80.25B6 (II) and were produced at the General Motors Research and Development Center. Buttons of the die-upset samples were prepared from overquenched ribbons using the melt-spun technique. Thin sections were cut from the buttons obtained by die-upset of the ribbons of I and II. These sections were mechanically polished and then ion milled until perforation. Electron microscopy was done using a JEM 2000FX microscope operating at 200 kV.