Anomalous Spin-Orbit Field via the Rashba-Edelstein Effect at the W / Pt Interface

We study the spin-orbit (SO) field in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$(Permalloy; Py)/$\mathrm{W}/\mathrm{Pt}$ trilayer by means of spin-torque ferromagnetic resonance, and demonstrate that the $\mathrm{W}/\mathrm{Pt}$ interface generates an extra SO field that acts on the Py layer. This unprecedented field originates from the following three processes: (1) spin accumulation at the $\mathrm{W}/\mathrm{Pt}$ interface via the Rashba--Edelstein effect, (2) diffusive spin transport in the W layer, and (3) spin absorption into the Py layer through accumulation at the Py/$\mathrm{W}$ interface. Our results mean that we can create an extra SO field away from the ferromagnet/metal interface and control its strength by a combination of two different metals.