Relation between unidirectional magnetoresistance and magnon generation by spin current*

Ferromagnet/spin Hall effect (SHE) material bialyers are central to modern active nanomagnetic devices. The unidirectional magnetoresistance (UMR) observed in such structures – the asymmetry of resistance with respect to the current direction – has been explained in terms of spin-dependent electronic transport [1], or alternatively the effects of SHE-induced magnon generation [2].
We report on electrical measurements of UMR in a Permalloy/Pt bilayer, performed in conjunction with magneto-optical Brillouin light spectroscopy of spin current-driven magnon population. We show that the current dependence of UMR closely follows the dipolar magnon density, and that both dependences exhibit the same scaling over a large temperature range of 80-400 K. These findings demonstrate a close relationship between spin current-driven magnon generation and UMR, and indicate that the latter is likely dominated by the dipolar magnons. Our results may facilitate the development of new magnetoelectronic approaches for the characterization of SHE-induced magnetization dynamics.

[1] C. O. Avci et al., Nat. Phys. 11, 570 (2015).
[2] S. Langenfeld et al., APL 108, 192402 (2016); T. Li et al., Appl. Phys. Expr. 10, 073001 (2017).