Element-Specific Magnetic Domain Imaging of (Nd, Dy)-Fe-B Sintered Magnets Using Scanning Transmission X-Ray Microscopy

We demonstrate an element-specific observation of magnetic domains in thermally demagnetized Nd-Fe-B and (Nd, Dy)-Fe-B sintered magnets using scanning transmission X-ray microscopy (STXM). Clear chemical and magnetic contrast images with the 30-nm spatial resolution were taken by STXM. Both maze-like magnetic domains and stripe magnetic domains with their widths of 200-300 nm are observed in both Nd-Fe-B and (Nd, Dy)-Fe-B sintered magnets. In both sintered magnets, multidomain structures are mostly formed within each grain-that is, magnetic domains are likely to be terminated at the grain boundaries. Stripe domains are originated from the grains with the (001)-axis misoriented to the sample normal. From the comparison between chemical and magnetic images, it is found that no clear magnetic domain is observed in Nd-rich phase at grain boundary triple points. Furthermore, it is also found that the interface between Nd2Fe14B phase and Nd-rich phase is chemically abrupt. Similar magnetic domain patterns are observed in Nd-Fe-B and (Nd, Dy)-Fe-B sintered magnets.