It has been predicted that transverse spin current can propagate coherently
(without dephasing) over a long distance in antiferromagnetically ordered
metals. Here, we estimate the dephasing length of transverse spin current in
ferrimagnetic CoGd alloys by spin pumping measurements across the compensation
point. A modified drift-diffusion model, which accounts for spin-current
transmission through the ferrimagnet, reveals that the dephasing length is
about 4-5 times longer in nearly compensated CoGd than in ferromagnetic metals.
This finding suggests that antiferromagnetic order can mitigate spin dephasing
-- in a manner analogous to spin echo rephasing for nuclear and qubit spin
systems -- even in structurally disordered alloys at room temperature. We also
find evidence that transverse spin current interacts more strongly with the Co
sublattice than the Gd sublattice. Our results provide fundamental insights
into the interplay between spin current and antiferromagnetic order, which are
crucial for engineering spin torque effects in ferrimagnetic and
antiferromagnetic metals