JUMPS OF MAGNETIC-POLARIZATION IN SM2CO17-BASED MAGNETS

At temperatures below 8.2 K large spontaneous jumps in the demagnetiza tion curve of Sm2(Co,Cu,Fe,Zr)17 magnets with high coercivity were det ected. For different samples no correlations concerning the onset, the depth or the number of jumps could be observed. Systematic investigat ions showed the following results: i) The emergence and the number of jumps depend on the temperature, the field sweeping rate and the sampl e dimensions. ii) The onset of jumps is shifted to smaller applied fie lds with decreasing temperature. iii) The cooling conditions have a st rong influence. These results have definitely shown that the observed polarization jumps are due to thermal instabilities because of the sma ll heat capacity and poor thermal conductivity in agreement with a loc al heating model.