We report on a measurement of the highly forbidden 6s^2 ^1S_0 \to 5d6s ^3
D_1 magnetic-dipole transition in atomic ytterbium using the
Stark-interference technique. This amplitude is important in interpreting a
future parity nonconservation experiment that exploits the same transition. We
find ∣∣ = 1.33(6)Stat​(20)β​×10−4μ0​, where the larger uncertainty comes from the previously
measured vector transition polarizability β. The M1 amplitude is small
and should not limit the precision of the parity nonconservation experiment.Comment: 4 pages, 5 figures Paper resubmitted with minor corrections and
additions based on comments from referee