Nonsinusoidal angular dependence of FMR-driven spin current across an antiferromagnet in Y 3 F e 5 O 12 / NiO / Pt trilayers

The out-of-plane angular (${\ensuremath{\theta}}_{\mathrm{H}}$) dependence of the inverse spin Hall effect (ISHE) voltage (${V}_{\mathrm{ISHE}}$) generated by spin pumping has been investigated in ${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$ (YIG)/NiO/Pt trilayers. A simple sinusoidal angular dependence of ${V}_{\mathrm{ISHE}}$ has been viewed as a signature of spin pumping. Surprisingly, we observe an extensive plateau in the ${V}_{\mathrm{ISHE}}$ vs ${\ensuremath{\theta}}_{\mathrm{H}}$ plots with a pronounced peak feature at ${\ensuremath{\theta}}_{\mathrm{H}}\ensuremath{\sim}{45}^{\ensuremath{\circ}}$ to ${60}^{\ensuremath{\circ}}$ when the measurement temperature is close to the N\'eel temperature $({T}_{\mathrm{N}})$ of NiO. This phenomenon can be understood as arising from the competition between the exchange coupling at the YIG/NiO interface, the easy-plane and in-plane easy-axis anisotropies of NiO, and the effect of the applied magnetic field. While insulating antiferromagnetic films can efficiently transmit spin currents and show promise for integration in spintronic devices, the underlying physics of spin ordering and dynamics is richer than currently understood.