  Self-induced spin-orbit torques (SI-SOTs) in ferromagnetic (FM) layers have
been overlooked when estimating the spin Hall angle (SHA) of adjacent
nonmagnetic (NM) layers. In this work, we observe anomalous sign inversion of
the total SOT in the spin-torque ferromagnetic resonance due to the enhanced
SI-SOT, and successfully rationalize the sign inversion through a theoretical
calculation considering the SHE in both the NM and FM layers. The findings show
that using an FM layer whose SHA sign is the same as that of the NM achieves
efficient SOT-magnetization switching with the assistance of the SI-SOT. The
contribution of the SI-SOT becomes salient for a weakly conductive NM layer,
and conventional analyses that do not consider the SI-SOT can overestimate the
SHA of the NM layer by a factor of more than 150.
