A nanocomposite Sm2Co17/Co magnet with a composition of Sm7Co93 was prepared by mechanical alloying. A domain–wall pinning mechanism was found to be dominant in the magnet, as investigated using Kronmüller’s micromagnetic theory. Transmission electron microscopy micrographs indicate that the half width between neighboring Co grains is about 40 nm. This value is two times larger than the range factor, r0, obtained from Kronmüller’s model. It appears that crystallographic defects other than the cobalt particles also play an important role in coercivity. © 1997 American Institute of Physics.