A research group has succeeded in measuring the spin transition in a thin film of certain molecules – a well-known material in organic light-emitting diodes – at room temperature. They found that this thin molecular film has a spin-diffusion length of about 62 nm, a length that could have practical applications in the development of bottom electronics technology. In addition, while electricity has been used to control spin transport in the past, the thin molecular film used in this study is photoconductive, allowing spin transport to be controlled using visible light.
Information processing devices – such as smartphones – are becoming more complex because their information-recording density is constantly increasing, thanks to advances in microfabrication technology. However, in recent years, the physical limits of processing are rapidly approaching, making further miniaturization difficult. Perhaps, though, the continued demand for more advanced technology requires a fundamental change in operating principles, so that new, faster and smaller devices can continue to be manufactured.
To meet this demand, a technology called spintronics — which uses the magnetic spin and charge of electrons — is attracting attention as a key technology, one that could unlock the next generation of advanced electronics. By aligning the direction of magnetic spin and moving it like an electric current, it is possible to propagate information using very little energy and generating less heat.
A research group, led by Professors Eiji Shikoh and Yoshio Takei of the Graduate School of Engineering at Osaka Metropolitan University, has successfully measured spin transport, at room temperature, in a thin film of molecules of alpha-naphthyl diamine derivative (?NPD), a well. – a well-known substance in organic light-emitting diodes. This thin molecular film was found to have a spin-diffusion length of about 62 nm, which is the distance they expect to be used in practical applications.
To use spin transport to develop spintronics technology, spin diffusion length in the range of tens of nanometers at room temperature is required for microprocessing. The NPD molecular thin film with a spin-diffusion length of 62 nm—a long distance for macromolecular materials—was fabricated for this study by thermal evaporation in vacuum. While electricity has been used to control rotational transport in the past, this new NPD molecular thin film is photoconductive, making it possible to control rotational transport using visible light.
“For practical use, it will be necessary to reveal more details about the mechanisms of spin transport and spin injection through thin molecular membranes to control spin transport,” noted Professor Shikoh. “Further research is expected to lead to ultra-energy-efficient devices that use small amounts of energy and have little risk of overheating.”