Geometrically Tunable Spin Superfluidity and Nonlocal Spin Hall Magnetoresistance in Devices Based on Easy Plane Magnetic Films

Spin superfluidity (SSF) invovles the near-dissipationless transport of spin angular momentum via a coherently precessing spin spiral [1], making it a promising route towards magnetic analogs of superconducting devices, as well as novel spintronics devices [2]. While conventional easy-plane magnets can exhibit SSF in theory [3], the required device geometries are incompatible with current fabrication methods and/or spin injection via the spin Hall effect in an adjacent heavy metal. Considering the ideal case of an insulating magnet, we analyze the nonlocal spin and charge transfer efficiencies of SSF devices with a lateral geometry [4], which has been underexplored due to an absence of compatible materials. Using a hydrodynamic formulation of the Landau–Lifshitz–Gilbert equation in conjunction with magneto-circuit theory, we show that the spin transfer efficiency is maximized when the area of the injector is much larger than the combined area of the detector and transport channel. Moreover, we recast the nonlocal resistance at the detector in terms of the spin transfer efficiency, spin Hall magnetoresistance (SMR) at the heavy metal/insulator interfaces, and the SOT efficiency. Our analysis demonstrates that SMR is inherently a nonlocal phenomenon and reveals the unrecognized Onsager reciprocal of the conventional effect: spin-pumping–induced SMR.

[1] E. B. Sonin, Adv. Phys. 59, 181 (2010). [2] D. Hill et al., Phys. Rev. Lett. 121, 037202 (2018) [3] S. Takei et al., Phys. Rev. Lett. 112, 227201 (2014)