Experiments on RCO5and related compounds with permanent magnet properties

This paper investigates the possibility of replacing the expensive rare-earth metals by the relatively inexpensive cerium mischmetal in rare-earth-cobalt permanent magnets. Using mischmetal, it is possible to obtain powders with coercivities as high as when pure cerium or lanthanum are used, although it is not possible to equal the values obtained with samarium. A compact with a density of 5.3 g.cm
^-3
gives a
(BH)_{\max}
of 3.1 MG.Oe, and if the special methods for obtaining high densities used by Buschow et al. or by Das were applied there seems no reason why values exceeding 10 MG-Oe should not be obtained. There are, however, some rather peculiar changes which occur in the compacts, especially when they are heated to about 150°C. It is not possible simply to replace cerium by mischmetal in the solid alloys of cobalt-cerium-copper described by Nesbitt as the response to heat treatment is quite different.