Long-range exchange spin transport in ferromagnetic nanowires driven by spin Hall current

Magnetic materials with easy plane magnetic anisotropy are predicted to support long-range spin currents via an exchange-dominated mode described by large-amplitude order parameter winding around the hard anisotropy axis. This mode is often referred to as spin superfluid due to similarity of the order parameter of this classical state to the order parameter of a quantum superfluid. In contrast to spin waves showing exponential spatial decay, this topologically protected exchange mode decays as a power law and thus is expected to support long-range spin currents. Here we use micromagnetic simulations to demonstrate the excitation of this exchange mode in a ferromagnetic nanowire by local injection of spin Hall current into the nanowire. The required easy plane anisotropy is engineered via tuning the values of perpendicular magnetic anisotropy and magnetic shape anisotropy in the nanowire geometry. We explore the dependence of the magnetic ground and excited states of the nanowire on the device and material parameters, and identify the parameter space supporting the long-range spin current. We conclude that this state is practically achievable in nanowires of common ferromagnetic materials.