  We systematically investigate the perpendicular magnetocrystalline anisotropy
(MCA) in Co$-$Pt/Pd-based multilayers. Our magnetic measurement data shows that
the asymmetric Co/Pd/Pt multilayer has a significantly larger perpendicular
magnetic anisotropy (PMA) energy compared to the symmetric Co/Pt and Co/Pd
multilayer samples. We further support this experiment by first principles
calculations on the CoPt$_2$, CoPd$_2$, and CoPtPd, which are composite bulk
materials that consist of three atomic layers in a unit cell, Pt/Co/Pt,
Pd/Co/Pd, Pt/Co/Pd, respectively. By estimating the contribution of bulk
spin-momentum coupling to the MCA energy, we show that the CoPtPd multilayer
with the symmetry breaking has a significantly larger perpendicular magnetic
anisotropy (PMA) energy than the other multilayers that are otherwise similar
but lack the symmetry breaking. This observation thus provides an evidence of
the PMA enhancement due to the structural inversion symmetry breaking and
highlights the asymmetric CoPtPd as the first artificial magnetic material with
bulk spin-momentum coupling, which opens a new pathway toward the design of
materials with strong PMA.
