Enhancement of Spin Currents in a Paramagnetic Lattice

A fundamental feature of spin currents is that spin, at variance from electric charge, is a non-conserved quantity. For this reason, a pure spin current is, typically, rapidly dissipated by irreversible spin-dependent scattering. We show that non-conservation of spin can be exploited to \textit{enhance} spin currents injected into a paramagnetic lattice of mutually interacting localized magnetic moments. The enhancement is due to the exchange interaction between the lattice sites and the non vanishing spin density associated with the spin current, which partially aligns the magnetic moments of the lattice. We also discuss how such enhanced spin currents could be exploited to increase the spin-transfer torque exerted on a ferromagnetic layer.