Direct observation of magnetization reversal in thin Nd2Fe14B film

By utilizing a sharp magnetic needle made of a sintered Nd2Fe14B permanent magnet, we were able to produce a strong magnetic field of up to approximately 560kA∕m in a transmission electron microscope and succeeded in observing the magnetization reversal in a thin film of sintered Nd2Fe14B by in situ Lorentz microscopy. The increase in the magnetic field induced by the magnetic needle led to a pair of straight magnetic domain walls forming abruptly from the grain boundary. The successive nucleation in the neighboring grain started at the grain boundary adjacent to the magnetic domain wall formed first. Eventually, the magnetic domain walls in the neighboring grains connected and moved continuously and finally disappeared.