Structural Phase Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin Film Heterostructure

TL;DR

This study reports a giant interfacial spin transparency in W/CoFeB heterostructures, strongly dependent on tungsten's structural phase, which enhances the efficiency of pure spin current generation for spintronic applications.

Contribution

It reveals a giant interfacial spin transparency in eta-W/CoFeB heterostructures and links it to tungsten's structural phase transition, advancing understanding of spin transport mechanisms.

Findings

Giant T of 0.81 in eta-W/CoFeB interface.

Strong dependence of spin transparency on W's structural phase.

Negligible effects of spin memory loss and two-magnon scattering.

Abstract

Pure spin current has transfigured the energy-efficient spintronic devices and it has the salient characteristic of transport of the spin angular momentum. Spin pumping is a potent method to generate pure spin current and for its increased efficiency high effective spin-mixing conductance (Geff) and interfacial spin transparency (T) are essential. Here, a giant T is reported in Sub/W(t)/Co20Fe60B20(d)/SiO2(2 nm) heterostructures in \beta-tungsten (\beta-W) phase by employing all-optical time-resolved magneto-optical Kerr effect technique. From the variation of Gilbert damping with W and CoFeB thicknesses, the spin diffusion length of W and spin-mixing conductances are extracted. Subsequently, T is derived as 0.81 \pm 0.03 for the \beta-W/CoFeB interface. A sharp variation of Geff and T with W thickness is observed in consonance with the thickness-dependent structural phase transition and resistivity of W. The spin memory loss and two-magnon scattering effects are found to have negligible contributions to damping modulation as opposed to spin pumping effect which is reconfirmed from the invariance of damping with Cu spacer layer thickness inserted between W and CoFeB. The observation of giant interfacial spin transparency and its strong dependence on crystal structures of W will be important for pure spin current based spin-orbitronic devices.