  We study the contribution to the proton's magnetic moment from a heavy quark
sea in quantum chromodynamics. The heavy quark is integrated out perturbatively
to obtain an effective dimension-6 magnetic moment operator composed of three
gluon fields. The leading contribution to the matrix element in the proton
comes from a quadratically divergent term associated with a light-quark tensor
operator. With an approximate knowledge of the proton's tensor charge, we
conclude that a heavy sea-quark contribution to the proton's magnetic moment is
positive in the asymptotic limit. We comment on the implication of this result
for the physical strange quark.
