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

Abstract

Pure spin current has transformed the research field of conventional spintronics due to its various advantages, including energy efficiency. An efficient mechanism for generation of pure spin current is spin pumping, and high effective spinmixing conductance (G eff ) and interfacial spin transparency (T) are essential for its higher efficiency. By employing the time-resolved magneto-optical Kerr effect technique, we report here a giant value of T in substrate/W (t)/Co 20 Fe 60 B 20 (d)/SiO 2 (2 nm) thin-film heterostructures in the beta-tungsten (β-W) phase. We extract the spin diffusion length of W and spin-mixing conductance of the W/CoFeB interface from the variation of damping as a function of W and CoFeB thickness. This leads to a value of T = 0.81 ± 0.03 for the β-W/CoFeB interface. A stark variation of G eff and T with the thickness of the W layer is obtained in accordance with the structural phase transition and resistivity variation of W with its thickness. Effects such as spin memory loss and two-magnon scattering are found to have minor contributions to damping modulation in comparison to the spin pumping effect which is reconfirmed from the unchanged damping constant with the variation of Cu spacer layer thickness inserted between W and CoFeB. The giant interfacial spin transparency and its strong dependence on crystal structures of W will be important for future spin-orbitronic devices based on pure spin current.

All‐Optical Detection of Spin Pumping and Giant Interfacial Spin Transparency in Co2Fe0.4Mn0.6Si/Pt Heterostructure

“…Whereas the spin‐orbit coupling at the interface or proximity induced interfacial depolarization leads to the SML and consequent enhancement of damping, the creation of degenerate magnon modes from an initially uniform FMR mode caused by the surface inhomogeneity scattering centers, leads to TMS effect. [ 57 ] Inclusion of these two effects into the effective damping gives the following modified set of expressions [ 19,58 ] $$\begin{equation}{\alpha _{{\rm{eff}}}} = {\alpha _0} + {\alpha _{{\rm{SP}}}} + {\alpha _{{\rm{SML}}}} + {\alpha _{{\rm{TMS}}}}\end{equation}$$ $$\begin{equation} \def\eqcellsep{&}\begin{array}{*{20}{c}} {{\alpha _{{\rm{eff}}}} = {\alpha _0} + \frac{{g{{{\mu}}_{\rm{B}}}}}{{4{{\pi}}d{M_{{\rm{eff}}}}{\rm{\ }}}}\left( {{G_{{\rm{eff}}}} + {G_{{\rm{SML}}}}} \right) + \frac{{{\beta _{{\rm{TMS\ }}}}}}{{{d^2}}}} \end{array} \end{equation}$$…”

“…Whereas the spin-orbit coupling at the interface or proximity induced interfacial depolarization leads to the SML and consequent enhancement of damping, the creation of degenerate magnon modes from an initially uniform FMR mode caused by the surface inhomogeneity scattering centers, leads to TMS effect. [57] Inclusion of these two effects into the effective damping gives the following modified set of expressions [19,58] 𝛼 eff = 𝛼 0 + 𝛼 SP + 𝛼 SML + 𝛼 TMS ( 15)…”

“…[ 18 ] Therefore, from an application viewpoint, a large value of interfacial spin transparency is the key for improved device efficiency. [ 19 ]…”

“…[18] Therefore, from an application viewpoint, a large value of interfacial spin transparency is the key for improved device efficiency. [19] Very few reports are available in the literature exploring the potential of Heusler compound and heavy metal heterostructure in effective spin current manipulation using spin pumping. [20,21] Cobalt-based Heusler compounds are promising half-metallic materials [22] which gained considerable interest [23] for their application potential in tunnel magnetoresistance (TMR) devices, [24,25] spin-torque nano oscillator (STNO) with low switching current [26,27] etc.…”

“…More recently, the all-optical time-resolved magneto-optical Kerr effect (TRMOKE) has been used as a reliable and non-invasive technique to probe spin pumping including spin-mixing conductance, spin-diffusion length, and interfacial spin transparency in FM/NM heterostructures. [19,35] This technique is devoid of any complex microfabrication of delicate waveguide structures. Besides, local measurement of magnetization dynamics directly in the time domain gives it a significant advantage in precise and reliable determination of magnetic damping parameter over the alternative techniques.…”