Unconventional Spin Currents Generated by the Spin-Orbit Precession Effect in Perpendicularly Magnetized Co−Tb Ferrimagnetic System

Charge-spin interconversion via spin-orbit coupling (SOC) provides an effective way to generate spin currents for electrical control of nanomagnets for data storage and processing. Except for the widely studied giant spin Hall effect (SHE) and Rashba-Edelstein effect (REE) that can generate a spin current with in-plane transverse spin polarization, theoretically proposed spin swapping or spin-orbit precession effect (SOPE) also can substantially generate spin currents with different spin polarizations in magnetic multilayers. Here, we experimentally demonstrate that except the SHE-induced large effective SOT ${\ensuremath{\theta}}_{y}^{\mathrm{eff}}\ensuremath{\sim}0.10\ensuremath{-}0.14$ comparable to the reported giant SHE \ensuremath{\beta}-phase $\mathrm{Ta}$, SOPE generated two considerable unconventional $\mathrm{SOTs}$ with in-plane longitudinal ${\ensuremath{\theta}}_{x}^{\mathrm{eff}}\phantom{\rule{0.25em}{0ex}}$ and out-of-plane spin polarizations ${\ensuremath{\theta}}_{z}^{\mathrm{eff}}$, which are also verified in a $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Tb}/\mathrm{Cu}/\mathrm{Py}$ trilayer structure. The former ${\ensuremath{\theta}}_{x}^{\mathrm{eff}}$ changes its sign with the unit magnetization reversal of the perpendicularly magnetized $\mathrm{Co}\text{\ensuremath{-}}\mathrm{Tb}$ layer, while the latter ${\ensuremath{\theta}}_{z}^{\mathrm{eff}}$ does not change its sign, consistent with the theoretical model of the SOPE mechanism. Our results pave an alternative way to design current-induced high-efficient SOT-based devices using abundant ferrimagnetic alloys.