Demagnetization curves of four rare-earth-cobalt magnet types at temperatures 300–1000 K

Intrinsic demagnetization curves and the temperature dependence of specific magnetization states were measured with a dc magnetometer on four types of sintered rare-earth-cobalt permanent magnets at temperatures from 300 to 1000 K. All magnetic properties vary reversibly with temperatures up to limits of 650–850 K, depending on the alloy. Precipitation-hardened magnets of the 1–7 or the 1–5 types and the common sintered SmCo5 all exhibit quite different temperature characteristics. The MHc of 1–7 type magnets decreases gradually with increasing temperature. Its temperature dependence can be well described by a simple exponential function. The MHc of SmCo5 drops sharply with increasing temperature and becomes very small at about 750 K. The cerium magnet shows a distinct kink in MHc versus T at 550 K, separating two temperature regions in which clearly different mechanisms are responsible for the coercivity.