  A spin current through a ferromagnet/heavy-metal interface may shrink due to
the spin-flip at the interface, resulting in the spin-memory loss. Here we
propose a mechanism of the spin-memory loss. In contrast to other mechanisms
based on interfacial spin-orbit coupling, our mechanism is based on the bulk
spin-orbit coupling in a heavy-metal. We demonstrate that the bulk spin-orbit
coupling induces the entanglement between the spin and orbital degrees of
freedom and this spin-orbital entanglement can give rise to sizable spin-flip
at the interface even when the interfacial spin-orbit coupling is weak. Our
mechanism emphasizes crucial roles of the atomic orbital degree of freedom and
induces the strong spin-memory loss near band crossing points between bands of
different orbital characters.
