  In spin transport experiments with spin currents propagating through
antiferromagnetic (AFM) material, the antiferromagnet is treated as a mainly
passive spin conductor not generating nor adding any spin current to the
system. The spin current transmissivity of the AFM NiO is affected by magnetic
fluctuations, peaking at the N\'eel temperature and decreasing by lowering the
temperature. In order to study the role of the AFM in local and nonlocal spin
transport experiments, we send spin currents through NiO of various thickness
placed on Y$_3$Fe$_5$O$_{12}$. The spin currents are injected either
electrically or by thermal gradients and measured at a wide range of
temperatures and magnetic field strengths. The transmissive role is reflected
in the sign change of the local electrically injected signals and the decrease
in signal strength of all other signals by lowering the temperature. The
thermally generated signals, however, show an additional upturn below 100$\,$K
which are unaffected by an increased NiO thickness. A change in the thermal
conductivity could affect these signals. The temperature and magnetic field
dependence is similar as for bulk NiO, indicating that NiO itself contributes
to thermally induced spin currents.
