  Magnetization switching using spin-orbit torque offers a promising route to
developing non-volatile memory technologies. The prerequisite, however, is the
charge-to-spin current conversion, which has been achieved traditionally by
harnessing the spin-orbit interaction in heavy metals, topological insulators,
and heterointerfaces hosting a high-mobility two-dimensional electron gas.
Here, we report the observation of charge-to-spin current conversion at the
interface between ferromagnetic Ni$_{0.8}$Fe$_{0.2}$ and ferroelectric
Bi$_{2}$WO$_{6}$ thin films. The resulting spin-orbit torque consists of
damping-like and field-like components, and the estimated efficiency amounts to
about 0.48 $\pm$ 0.02, which translates to 0.96 $\pm$ 0.04 nm$^{-1}$ in terms
of interfacial efficiency. These numbers are comparable to contemporary
spintronic materials exhibiting giant spin-orbit torque efficiency. We suggest
that the Rashba Edelstein effect underpins the charge-to-spin current
conversion on the interface side of Ni$_{0.8}$Fe$_{0.2}$. Further, we provide
an intuitive explanation for the giant efficiency in terms of the spin-orbit
proximity effect, which is enabled by orbital hybridization between W and Ni
(Fe) atoms across the interface. Our work highlights that Aurivillius compounds
are a potential addition to the emerging transition metal oxide-based
spin-orbit materials.
