The power factor for the Fe ion-implanted samples is greater than that of the pristine sample with a value of 700 mW m−1 K−2 at 420 K for the I1E15A sample.
Spin pumping has been considered a powerful tool to manipulate
the spin current in a ferromagnetic/nonmagnetic (FM/NM) system, where
the NM part exhibits large spin–orbit coupling (SOC). In this
work, the spin pumping in β-W/Interlayer (IL)/Co2FeAl (CFA) heterostructures grown on Si(100) is
systematically investigated with different ILs in which SOC strength
ranges from weak to strong. We first measure the spin pumping through
the enhancement of effective damping in CFA by varying the thickness
of β-W. The damping enhancement in the bilayer of β-W/CFA
(without IL) is found to be ∼50% larger than the Gilbert damping
in a single CFA layer with a spin diffusion length and spin mixing
conductance of 2.12 ± 0.27 nm and 13.17 ± 0.34 nm–2, respectively. Further, the ILs of different SOC strengths such
as Al, Mg, Mo, and Ta were inserted at the β-W/CFA interface
to probe their impact on damping in β-W/ILs/CFA. The effective
damping reduced to 8% and 20% for Al and Mg, respectively, whereas
it increased to 66% and 75% with ILs of Mo and Ta, respectively, compared
to the β-W/CFA heterostructure. Thus, in the presence of ILs
with weak SOC, the spin pumping at the β-W/CFA interface is
suppressed, while for the high SOC ILs effective damping increased
significantly from its original value of β-W/CFA bilayer using
a thin IL. This is further confirmed by performing inverse spin Hall
effect measurements. In summary, the transfer of spin angular momentum
can be significantly enhanced by choosing a proper ultrathin interface
layer. Our study provides a tool to increase the spin current production
by inserting an appropriate thin interlayer which is useful in modifying
the heterostructure for efficient performance in spintronics devices.
The spin pumping mechanism and associated interfacial Gilbert damping are demonstrated in ion-beam sputtered Co2FeAl (CFA)/Mo bilayer thin films employing ferromagnetic resonance spectroscopy. The dependence of the net spin current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement of the net effective Gilbert damping are reported. The experimental data has been analyzed using spin pumping theory in terms of spin current pumped through the ferromagnet/nonmagnetic metal interface to deduce the effective spin mixing conductance and the spin-diffusion length, which are estimated to be 1.16(±0.19)×10 19 m −2 and 3.50±0.35nm, respectively. The damping constant is found to be 8.4(±0.3)×10 -3 in the Mo(3.5nm) capped CFA(8nm) sample corresponding to a ~42% enhancement of the original Gilbert damping (6.0(±0.3)×10 -3 ) in the uncapped CFA layer. This is further confirmed by inserting a Cu dusting layer which reduces the spin transport across the CFA/Mo interface. The Mo layer thickness dependent net spin current density is found to lie in the range of 1-3 MAm -2 , which also provides additional quantitative evidence of spin pumping in this bilayer thin film system.
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