Angular Dependence of Spin Torques in Current-in-Plane Exchange-Biased Spin Valves

An in-plane charge current through a magnetic heterostructure with sizable spin-orbit coupling can generate spin torques (e.g. via the spin Hall effect). Recent studies have reported reduced crystal symmetry [1] or magnetic ordering [2,3] as a means of generating spin torques that are not possible with the conventional spin Hall effect.

Here, we investigate spin torques in current-in-plane NiFe/Cu/CoFe/IrMn spin valves. The exchange-biased CoFe layer provides the symmetry breaking necessary for unconventional spin torques. By employing spin-torque ferromagnetic resonance, we have measured spin torques in the NiFe free layer magnetized along different directions with respect to the CoFe fixed layer. Our angle-dependent results show expected torques from the Oersted field and spin/anomalous Hall effects, along with an additional torque that cannot be explained by existing predictions. Our work points to the possibility of generating a new family of unconventional torques in spin valves compatible with well-established device fabrication processes.

 

[1] D. MacNeill, et al., Nat. Phys. 13, 300 (2017)

[2] Y. Hibino, et al., Phys. Rev. B 101, 174441 (2020)

[3] S. C. Baek, et al., Nat. Mater. 17, 509 (2018)