Simultaneously Enhanced Spin Hall Effect and Spin-Mixing Conductance in a Y3Fe5O12 /bcc- W1−xCrx Heterostructure by Bulk Extrinsic Scattering and Interfacial Electric Field

Abstract

The spin-current efficiency in ferromagnet (FM)/nonmagnetic metal (NM) heterostructures is a key issue for many subcategories of spintronics, and it is determined by both the spin Hall angle $({\ensuremath{\theta}}_{\mathrm{SH}})$ of the NM and the spin-mixing conductance $({g}_{\ensuremath{\uparrow}\ensuremath{\downarrow}})$ related to the constituents and, in particular, to the interface. Here, we study spin transport in the ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}(\mathrm{YIG})$/${\mathrm{W}}_{1\text{\ensuremath{-}}x}{\mathrm{Cr}}_{x}$ heterostructure over the full composition by means of the spin Seebeck effect and spin pumping. An appreciably enhanced inverse spin Hall voltage is observed for the substitutional alloy of bcc-$\mathrm{W}$ and $\mathrm{Cr}$, with the maximum obtained at an equiatomic composition. We find that the ${\ensuremath{\theta}}_{\mathrm{SH}}$ of bcc-${\mathrm{W}}_{0.5}{\mathrm{Cr}}_{0.5}$ is 1.3 times as large as that of \ensuremath{\beta}-$\mathrm{W}$, which mainly originates from intensively disordered atomic scattering. More significantly, $\mathrm{YIG}$/bcc-${\mathrm{W}}_{0.5}{\mathrm{Cr}}_{0.5}$ has a ${g}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ value of $1.42\phantom{\rule{0.25em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.25em}{0ex}}{10}^{18}\phantom{\rule{0.25em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$, which is more than twice that for $\mathrm{YIG}$/\ensuremath{\beta}-$\mathrm{W}$ ($5.98\phantom{\rule{0.25em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.25em}{0ex}}{10}^{17}\phantom{\rule{0.25em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$). Meanwhile, a sizable interfacial electric field is identified in $\mathrm{YIG}$/\ensuremath{\beta}-$\mathrm{W}$, but not in $\mathrm{YIG}$/bcc-${\mathrm{W}}_{0.5}{\mathrm{Cr}}_{0.5}$, showing strong correlation between ${g}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ and the interfacial electric field. This work not only provides a readily achievable alloy with ${\ensuremath{\theta}}_{\mathrm{SH}}$ exceeding that of the metastable \ensuremath{\beta}-$\mathrm{W}$, but also implies the possibility of manipulating ${g}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ via Rashba-type spin-orbit coupling by engineering an interfacial electric field in insulating FM/NM heterostructures.