  We investigate the role of hyperfine mixing in the electromagnetic decay of
ground state doubly heavy $bc$ baryons. As in the case of a previous
calculation on $b\to c$ semileptonic decays of doubly heavy baryons, we find
large corrections to the electromagnetic decay widths due to this mixing.
Contrary to the weak case just mentioned, we find here that one can not use
electromagnetic width relations obtained in the infinite heavy quark mass limit
to experimentally extract information on the admixtures in a model independent
way.
