A new device has been developed to take advantage of the spin of electrons that could significantly improve upon the energy efficiency of a range of electronic devices. Researchers have presented a three-layer insulating structure that can operate as a scalable pure spin current device, an essential ingredient in spintronics.
In the study, which was led by scientists from the University of California, Riverside, and reported in the journal Nature Communications [Li et al. Nat. Commun. (2016) DOI: 10.1038/ncomms10858], the transmission of electrical signals through insulators in a sandwich-like structure was shown for the first time. Standard electronic devices depend on the transport of electrons in a semiconductor such as silicon; however, studies have been increasingly used the spin of an electron instead of its charge to devise new spintronic devices that can be more energy efficient and versatile than those in typical silicon chips and circuit elements.
"This is a proof-of-concept experiment that demonstrates the feasibility of using pure spin currents in scalable devices"Jing Shi
Spintronics uses spin-polarized charge currents, with the magnon-mediated current drag effect able to be switched on and off by altering the state of the magnetization in the magnetic insulator layer. To produce the device, the team used a high-quality magnetic insulator grown on metal that was fully insulated to avoid any signal leakage. Based on both sputtering for metals and pulsed laser deposition for the insulator, they demonstrated that the magnetic insulator, which was 50–100 nanometer thick, is of sufficient high quality when grown on 5 nanometer thick platinum, as well as being both magnetic and insulating.
In the structures, a magnetic insulator is sandwiched between two different metals. The metals help generate and detect spin current, and it was also shown that the signal transmission could be switched on and off and modulated in its strength based on the magnetic state, or direction of the magnetization, of the magnetic insulators. The direction of the magnetization can therefore be viewed as a memory state of non-volatile random access memory devices, while the signal level can also be modulated through altering the direction of the magnetization, allowing it to be used for analog devices. It is possible for the structure to be reduced through nanofabrication to help scale down the devices.
As researcher Jing Shi explained, “This is a proof-of-concept experiment that demonstrates the feasibility of using pure spin currents in scalable devices”. In terms of the fundamental science, there is much more to explore, including the decay of the magnons in magnetic insulators and the efficiency of spin current interconversion at the interfaces, an understanding of which could lead to potential device applications.