Effect of annealing conditions on the microstructure and magnetic properties of sintered Nd-Fe-B magnets as seen by magnetic smallangle neutron scattering

We have investigated the effect of the annealing conditions (heating rate and temperature) on themagnetic microstructure of sintered Nd-Fe-B magnets by means of magnetometry, scanning electronmicroscopy, high-energy synchrotron x-ray diffraction, and small-angle neutron scattering (SANS).While the temperature treatment has a strong effect on the coercivity (reduction by about 50% onannealing), the associated changes in the microstructure do surprisingly not show up (or at best onlyvery weakly) in the neutron-scattering signal, which probes a mesoscopic real-space length scaleranging between about 1–300 nm. On the other hand, the x-ray data reveal microstructural changes inthe Nd-rich phases, presumably due to modifications in grain-boundary regions. Moreover, weobserve an unusual diamond-shaped angular anisotropy in the SANS cross section, which stronglypoints towards the existence of texture in the nuclear microstructure