Theoretical research by A*STAR researchers in Singapore shows that spin-polarized current can simply be achieved by applying an oscillating voltage across the device. Spin-polarized is critical for Spintronics devices, but imperfections in a material can easily destroy the polarization.

The researchers looked at a two-dimensional electron gas (in which the electrons can move only in one plane). If you pass a spin-polarized current through this gas, a Rashba spin-orbit coupling effect makes the spin change (first upwards and then downwards) - which reduces the polarization to zero. Using a spin-current rectifier (like a spin polarization filter) one can control the strength of the Rashba coupling effect and so prolong the spin current's polarization life.

The researchers built a model that shows that when the frequency of the voltage is zero, the spin polarization goes back and forth as expected. But if the frequency is increased, there's an asymmetrical pattern of oscillation in favor of positive polarization. They call this a "gradual process of rectification". If the external modulation frequency is much faster than the natural precessional frequency of the spins (the Larmor frequency), the spins have no time to change direction and so remain pointing upwards - and so there's a spin-polarized current.

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