Anomalous demagnetization process at very low temperature in Nd‐Fe‐B magnets

Both Nd15Fe77B8 and Sm(CoCu)5 sintered magnets have been reported to exhibit staircase hysteresis loops with giant Barkhausen jumps below about 10 K. The pattern is reproducible at a fixed temperature. Here the observation of heat pulses associated with the magnetization jumps in Nd15Fe77B8 magnets is reported. The origin of these Barkhausen jumps in sintered magnets is discussed as a two‐stage trigger/propagation process. The first stage may be dominated by magnetization reversal in volumes of δ3, where δ is the domain‐wall thickness, as in the magnetic after effect, whereas the second stage reflects thermally induced domain‐wall motion facilitated by the small lattice specific heat below about 10 K.