of spins at the Fermi level. In addition, low magnetic damping and expected high spin pumping makes Heusler alloys suitable for the interface spin transport study and pure spin current-based spin torque nano-oscillators \[16\]. There have been intense studies of spin dynamics with low damping materials, e.g. NiFe and CoFeB with various HM \[17$-$21\]. However, there are only a few reports on the spin dynamics of Heusler alloys with HM \[15,22\]. $Co_2Fe_{0.4}Mn_{0.6}Si$ (CFMS) is a Heusler alloy which shows low damping and 100$\%$ spin polarization \[23\]. Figure 1(a) shows a typical schematic for density of states for half metallic material. However, the spin pumping efficiency ($g_{r}^{\uparrow \downarrow}$) in CFMS/HM system has so far not been evaluated, which would help to understand its use for applications. Here, we report the spin pumping study in CFMS/Pt system with varying the thickness of Pt via (1) measurement of ISHE, (2) evaluation of effective mixing conductance $g_{r}^{\uparrow \downarrow}$ and (3) spin interface transparency.

EXPERIMENTAL DETAILS
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The bilayer samples viz. S1$\#$ CFMS(20 nm)/Pt(3 nm), S2$\#$ CFMS(20 nm)/Pt(5 nm), S3$\#$ CFMS(20 nm)/Pt(7 nm), S4$\#$ CFMS(20 nm)/Pt(10 nm) and S5$\#$ CFMS(20 nm)/Pt(20 nm) were prepared on MgO(100) substrates using dc magnetron sputtering in a vacuum system 