Researchers measure spin transport across molecular films

Thursday, 02 February, 2023

Researchers measure spin transport across molecular films

Information processing devices — such as smartphones — are becoming more sophisticated as their information processing density increases, due to advances in microfabrication technology. However, the physical limits to processing are approaching, making further miniaturisation difficult. The continued demand for more sophisticated technology requires a change in operating principles, so that faster, smaller devices can continue being made.

To meet this demand, a technology called spintronics — using the magnetic spin and the charge of electrons — could unlock the next generation of advanced electronics. By aligning the direction of a magnetic spin and moving it like an electric current, it is possible to propagate information using little power and generating less waste heat.

A research group, led by Professors Eiji Shikoh and Yoshio Teki of the Osaka Metropolitan University Graduate School of Engineering, has measured spin transport at room temperature in a thin film of alpha-naphthyl diamine derivative (αNPD) molecules, a well-known material in organic light-emitting diodes. This molecular thin film was found to have a spin diffusion length of approximately 62 nanometres, a distance that could be used in practical applications. To use spin transport to develop spintronics, technology requires a spin diffusion length in the tens of nanometre range at room temperature for accurate processing. The thin molecular film of αNPD with a spin diffusion length of 62 nanometres — a long distance for molecular materials — was fabricated for this study by thermal evaporation in vacuum. While electricity has been used to control spin transport in the past, this new thin αNPD molecular film is photoconductive, making it possible to control spin transport using visible light.

Image caption: Schematic illustration of the spin transport demonstration of αNPD molecular thin film. A three-layered sample consisting of a ferromagnetic metal Ni-Fe alloy film, an αNPD molecular film, and a palladium (Pd) film, prepared by vacuum deposition. Using spin pumping driven by ferromagnetic resonance (FMR) in the Ni-Fe alloy thin film, a spin current generated from the Ni-Fe alloy film went through the αNPD film and passed to the Pd film. Image credit: Eiji Shikoh

“For practical use, it will be necessary to uncover more details about spin injection and spin transport mechanisms through thin molecular films to control spin transport. Further research is expected to lead to the realisation of super energy-efficient devices that use small amounts of power and have little risk of overheating,” Shikoh said.

The research findings were published in Solid State Communications.

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