Evolution of interaction domains in textured fine-grained Nd2Fe14B magnets

The magnetic microstructure of thermomechanically processed (die-upset) melt-spun NdFeB magnets with different degrees of texture in thermally demagnetized and in dc-demagnetized states has been investigated systematically using magnetic force microscopy. An isotropic magnetic microstructure with a fine contrast on a scale between 200 and 400 nm has been clearly observed in the hot-pressed precursor in the thermally demagnetized state. Broad and well-pronounced interaction domains with lateral expansion over many individual grains have been found in the magnet with a maximum degree of texture. The crystallographic texture of this magnet has been analyzed by electron backscatter diffraction using a high-resolution scanning electron microscope. On a mesoscopic scale, most of the crystallites have a misorientation smaller than 10 deg, yielding macroscopically a high value of remanent magnetization (1.34 T). The presence of a threshold value in dependence of the size of the interaction domains on the degree of texture has been identified. The alignment of individual crystallites strongly influences the formation and the size of interaction domains.