Hall-Type and Unidirectional Spin Pumping

Abstract

Conventional spin pumping, driven by magnetization dynamics, is longitudinal since the pumped spin current flows normal to the interface between the ferromagnet and the conductor. We predict \textit{Hall-type/transverse} and \textit{unidirectional} spin pumping into conductors by near-field electromagnetic radiation emitted by, \textit{e.g.}, magnetization dynamics. The joint effect of the electric and magnetic fields results in a pure spin current flowing parallel to the interface, i.e., a Hall-type spin pumping, which is highly efficient due to the strong coupling to the electric field. Such a transverse spin current is unidirectional, with the spatial distribution controlled by the magnetization direction. Our finding reveals a robust approach for generating and manipulating spin currents in future low-dimensional spintronic and orbitronic devices.

Figures (5)

• Figure 1: Comparison of longitudinal [(a)] and transverse or Hall-type [(b)] spin pumping by magnetization dynamics of the ferromagnet "F" into the conductor "N". ${\bf M}_s$ denotes the magnetization of the magnet. The blue and red arrows indicate, respectively, the flow and spin-polarization directions of a spin current. ${\bf H}$ and ${\bf E}$ in (b) denote the stray magnetic and electric fields emitted by the magnetization dynamics.
• Figure 2: Spin current pumped by the joint effect of the electric and magnetic fields of the point light source in the 2DEG. (a) illustrates the flow and the spin-polarization directions. (b) shows the oscillation of $\rho|{\pmb{\cal J}}_{s}(\pmb{\rho})|$ away from the source.
• Figure 3: Pumping of transverse and longitudinal spin currents by the stray electromagnetic field. The thick red arrows indicate the spin-polarization direction, and the red curves denote the direction of electron propagation. Both the transverse and longitudinal spin currents are unidirectional.
• Figure 4: Transverse unidirectional spin current pumped by magnetization dynamics. (a) and (b) illustrate the spatial distribution of Hall spin current density pumped by a near electromagnetic field when ${\bf M}_s\parallel\hat{\bf y}$ and ${\bf M}_s\parallel -\hat{\bf y}$, respectively. The blue rectangular area indicates the region covered by the nanowire. (c) and (d) depict the asymmetric spin texture ${\bf S}_x(q_x,q_y)$ in the wave-vector space (normalized by its maximum value) that differ at $x<-w/2$ and $x>w/2$, demonstrating the physical origin of the Hall spin current with $\sum_{q_x}{\bf S}_x(q_x,q_y)>0$ [$\sum_{q_x}{\bf S}_x(q_x,q_y)<0$] for $q_y>0$ ($q_y<0$). Parameters used for calculation are given in the text.
• Figure 5: Unidirectional longitudinal spin current excited by a near chiral electromagnetic field. (a) and (b) illustrate the magnitude and spatial distribution of the longitudinal spin current density for ${\bf M}_s\parallel\hat{\bf y}$ and ${\bf M}_s\parallel -\hat{\bf y}$ with different electron densities.