As noted in Tech-On!, researchers at Tohoku University (Tohoku, Japan) and Japan Atomic Energy Agency (JAEA; Saitama, Japan) have discovered that a spin current can be generated by applying light to an insulating material.1 They also developed surface-plasmon-resonance-based technology to convert a spin current to an electric current.
A spin current is an element of spintronics, a mostly research-stage technology that relies on the electron's spin and magnetic moment, as well as its traditionally exploited charge, to enable practical semiconductor-based devices (memory storage devices have already been developed). The use of spin current as an intermediary step between light and electrical current is a new energy-conversion principle.
As an insulating material, they used a magnetic garnet (BiY2Fe5O12) thin film embedded with gold (Au) nanoparticles with a diameter of 100 nm or less. A platinum (Pt) thin film was coated on top of the garnet film.
When light with a wavelength of about 690 nm irradiates the device, a strong localized magnetic field is generated around the Au nanoparticles due to surface-plasmon resonance, exciting spin motions. The spin current injected into the Pt film is converted within the Pt to an electromotive force due to "inverse spin-Hall effects," which are related to quantum relativity theory.
In an experiment, the university and JAEA measured the electromotive force generated by the inverse spin-Hall effects and proved that the detected signals were derived from the spin current generated from the magnetic garnet. Through a simulation, they separated the effects of heat generated by the applied light.
The latest research results will contribute to the formation of a new research field combining surface-plasmon and spin current and the research and development of electrical/magnetic devices that do not require an external power source, says Tech-on!. For example, because a spin current can be generated from heat, sound waves, and other sources, it might become possible to realize a device that can use multiple energy sources including light at the same time.
1. Uchida K. et al., Nature Communications (2015); doi: 10.1038/ncomms6910