Mischmetal-cobalt as a permanent magnetic material

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Abstract
Permanent magnets based on MMCo5(MM=mischmetal) were produced by powder metallurgical means with a coercivity IHc=9 kOe, a remanence Br=7.8 kG, and an energy product of (BH)max=14.5 MG Oe. These values could be increased by substituting some MM by Sm and Nd. The influence of MM composition on both the primary magnetic properties, as measured on single crystals, and the secondary magnetic properties and their temperature dependences was studied. The saturation magnetization Ms, the remanence Br, and the anisotropy field Ha vary almost linearly with composition. In contrast, IHc showed a more complex compositional dependence; it increases with increasing La content, decreases with Ce and Pr content, and passes through a maximum with increasing Nd content. The temperature dependence of IHc reflects the temperature dependence of Ha from the different compositions. A two‐step postsintering heat treatment was developed which results in good hard magnetic properties. The first step of 1 h at 1250 K is a homogenizing treatment, the second step of 1 h at about 620 K seems to cause small 2‐17 precipitates to form which act as pinning centers.