Jumps of magnetic polarization in Sm2Co17-based magnets

At temperatures below 8.2 K large spontaneous jumps in the demagnetization curve of Sm₂(Co,Cu,Fe,Zr)₁₇ magnets with high coercivity were detected. For different samples no correlations concerning the onset, the depth or the number of jumps could be observed. Systematic investigations showed the following results: i) The emergence and the number of jumps depend on the temperature, the field sweeping rate and the sample dimensions. ii) The onset of jumps is shifted to smaller applied fields with decreasing temperature. iii) The cooling conditions have a strong influence. These results have definitely shown that the observed polarization jumps are due to thermal instabilities because of the small heat capacity and poor thermal conductivity in agreement with a local heating model