The temperature dependence of demagnetization of MMl−xSmxCo5

In permanent magnet applications such as electric motors, high reverse magnet fields are experienced by the magnet and a critical design parameter is the onset of the ’’knee’’ of the hysteresis loop. The associated field, H*, marks the onset of irreversible demagnetization. This is particularly important for mischmetal-based magnets which exhibit lower coercivity than SmCo5 magnets. This paper reports measurements of the demagnetization of sintered MMl−xSmxCo5 magnets for 0.02 ?x? 0.43 over the temperature range: 175 K ?T? 425 K. The compositions were formed by alloying ’’natural’’ and Ce-free mischmetal with varying percentages of samarium and then blending with a ’’sintering aid’’. The temperature dependence of H* can be described by H* (T2) = H* (T1) (1 − 0.004 (T2−T1)), where the temperature coefficient −4×10−3K−1 is independent of the composition and coercivity within the limits investigated.