Off-axis electron holographic mapping of magnetic domains in Nd2Fe14B

Off-axis electron holography employing a field-free Lorentz lens has been used to provide direct imaging of magnetic induction in Nd2Fe14B with nanometer-scale resolution and high signal-to-noise. Using this technique, reconstructed phase images have been used to measure domain wall widths for 90 degrees and 180 degrees walls in a sintered sample were measured to be no greater than 7 and 9 nm, respectively. Induction maps show an unusual array of 90 degrees domains in a hot-press sample, with singularities at the intersections of the domains. In situ thermal annealing of the hot-pressed sample resulted in magnetization rotation accompanied by domain wall movement and evidence for pinning at a structural defect. Heating of the sample above 400 degrees C resulted in the accumulation of small particles in thin regions and decrease in magnetic contrast. (C) 1998 American Institute of Physics. [S0021-8979(98)41411-7].