  The study of spin current efficiency in different materials is one of the
emergent research topics in modern days. Spin pumping and inverse spin Hall
effect (ISHE) are popular tools to study the spin to charge current conversion
efficiency in the materials. In last one decade, ISHE and spin pumping are
heavily investigated in ferromagnet (FM)/ heavy metal (HM) heterostructures.
Recently the antiferromagnetic (AFM) materials are found to be a good
replacement of heavy metals (HM) for these kind of studies. Faster dynamics,
exhibiting very high spin-orbit coupling, absence of stray field, efficient
propagation of spin current make AFM to be a good replacement of HMs.
Understanding the role of different FM layers in a FM/AFM heterostructure for
ISHE or spin pumping study is very important for spin to charge conversion
physics. In this context we have performed the ISHE in CoFeB/ IrMn
heterostructures. Spin pumping study is carried out for
$Co_{60}Fe_{20}B_{20}(12 nm)/ Cu(3 nm)/ Ir_{50}Mn_{50}(t nm)/ AlO_{x}(3 nm)$
samples where \textit{t} value varies from 0 to 10 nm. The Cu(3 nm) buffer
layer is used which is less than the spin diffusion length($\sim$8 nm) of Cu to
improve the IrMn growth. The 3 nm Cu layer allows the unperturbed spin current
propagation in the heterostructures. Damping of all the samples is higher than
the single layer CoFeB which indicates that the spin pumping is due to the
presence of IrMn. Further the spin pumping in the samples are confirmed by ISHE
measurement. The real part of spin mixing conductance (\textit{$g_{r}^{\uparrow
\downarrow}$}) = 0.704 $\pm$ 0.01 $\times$ $10^{18}$ $m^{-2}$ is found to be
maximum in IrMn(2 nm) sample from the ISHE analysis. The large Spin Hall angle
was also found to be $\sim$ 0.30 for all the samples.
