  Based on the spin-pumping theory and first-principles calculations, the
spin-mixing conductance (SMC) is theoretically studied for Pt/Permalloy
(Ni$_{81}$Fe$_{19}$, Py) junctions. We evaluate the SMC for ideally clean Pt/Py
junctions and examine the effects of interface randomness. We find that the SMC
is generally enhanced in the presence of interface roughness as compared to the
ideally clean junctions. Our estimated SMC is in good quantitative agreement
with the recent experiment for Pt/Py junctions. We propose possible routes to
increase the SMC in Pt/Py junctions by depositing a foreign magnetic metal
layer in Pt, offering guidelines for designing the future spintronic devices.
