Spin pumping and inverse spin Hall effect in CoFeB/IrMn heterostructures.

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.