Abstract
In an electron microscope study of aged Sm‐Co‐Cu–based magnetic materials with the Sm2Co17 structure, it is shown that the previously reported coercivities of these materials are a consequence of the presence of very fine precipitates of the Cu‐containing SmCo5 phase which act as pinning centers. In comparing the microstructures of alloys with different Sm/Co,Cu ratios, and with some Co replaced by Fe, a marked difference is observed both in the precipitate morphology and the fault density of the matrix phase. Possible reasons for this are discussed, and it is shown that the lattice misfit has a marked effect on the morphology.