  We investigate the effects of two-body currents on magnetic dipole moments of
medium-mass and heavy nuclei using the valence-space in-medium similarity
renormalization group with chiral effective field theory interactions and
currents. Focusing on near doubly magic nuclei from oxygen to bismuth, we have
found that the leading two-body currents globally improve the agreement with
experimental magnetic moments. Moreover, our results show the importance of
multi-shell effects for $^{41}$Ca, which suggest that the $Z=N=20$ gap in
$^{40}$Ca is not as robust as in $^{48}$Ca. The increasing contribution of
two-body currents in heavier systems is explained by the operator structure of
the center-of-mass dependent Sachs term.
