Independence of spin-orbit torques from the exchange bias direction in Ni₈₁Fe₁₉/IrMn bilayers

It has recently been demonstrated that metallic antiferromagnets have sizeable spin Hall effects [1,2] and therefore can act as active components in spintronics devices. At the same time, interfacial exchange coupling in ferromagnet (FM)/antiferromagnet (AF) bilayers are commonly used for generating reference magnetization directions. Here we investigated whether there is a direct correlation between exchange bias and spin orbit torques, since both are effects that rely on interfacial magnetic interactions. We fabricated Py (Ni₈₁Fe₁₉)/IrMn bilayers and used spin transfer torque ferromagnetic resonance measurements with different relative orientations between applied fields and exchange bias. These measurements revealed no significant dependence of spin orbit torques on the exchange bias field directions.
Supported by DOE-BES-MSE.
[1] W. Zhang et al., Phys. Rev. Lett. 113, 196602 (2014).
[2] W. Zhang et al., Phys. Rev. B 92, 144405 (2015).