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NUS scientists achieve breakthrough in development of next-generation memory technology

Associate Professor Yang Hyunsoo (left) and Dr Shawn Pollard (right), who are from the Department of Electrical and Computer Engineering at the NUS Faculty of Engineering, are key members of a research team that invented a novel ultra-thin multilayer film which could harness the properties of skyrmions as information carriers for storing and processing data on magnetic media (Image credit: Siew Shawn Yohanes)

With accelerated technological development and explosion in the volume of data produced, there is a surge in demand for materials and techniques for storing of large volumes of data and improved data processing. A team of scientists at the National University of Singapore (NUS) has invented an ultra-thin multilayer film, which could enable design of data storage devices, that use less power and work faster than existing memory technologies. The film harnesses the properties of tiny magnetic whirls or vortices, known as skyrmions, as information carriers for storing and processing data on magnetic media.

The team was led by Associate Professor Yang Hyunsoo from the Department of Electrical and Computer Engineering at the National University of Singapore’s (NUS) Faculty of Engineering and it developed the film in collaboration with researchers from Brookhaven National Laboratory, Stony Brook University, and Louisiana State University. The invention was reported in prestigious scientific journal, Nature Communications, on 10 March 2017. The technology

Scientists predicted the existence of skyrmions in 1962, but they were discovered experimentally in magnetic materials only in 2009. Magnetic skyrmions can be used as bits to store information in next-generation memory and logic devices, where the state of the bit is encoded by the existence or non-existence of the magnetic skyrmion.

While the magnetic information encoded by skyrmions is robust due to the the strong forces that lock magnetic fields into the skyrmion pattern, scientists can move a skyrmion with significantly less energy than is needed to move a ferromagnetic domain, the objects currently used in the memory devices in our computers and smartphones.

The press release explains that Skyrmions have been shown to exist in layered systems, with a heavy metal placed beneath a ferromagnetic material. Due to the interaction between the different materials, an interfacial symmetry breaking interaction (known as the Dzyaloshinskii-Moriya interaction (DMI)), is formed and it helps to stabilise a skyrmion.

However, there were two challenges: the stability of the skyrmion is compromised in the absence of an out-of-plane magnetic field present; 2) it is difficult to image the nano-sized materials. To address these limitations, the researchers worked towards creating stable magnetic skyrmions at room temperature, without the need for a biasing magnetic field.

The experiments

The NUS team discovered that a DMI (the stabilising factor) could be maintained in multilayer films composed of cobalt and palladium, large enough to stabilise skyrmion spin textures.

The NUS researchers in collaboration with Brookhaven National Laboratory in the United States, found that they could use Lorentz transmission electron microscopy (L-TEM) to obtain clear contrast consistent with that expected for skyrmions, with sizes below 100 nanometres, by tilting the film with respect to the electron beam.Dr Pollard explained that the presence of DMI in a symmetric structure like the one present in their work was unexpected. Moreover, the nanoscale skyrmions persisted even after the removal of an external biasing magnetic field.

Assoc Prof Yang said, “This experiment not only demonstrates the usefulness of L-TEM in studying these systems, but also opens up a completely new material in which skyrmions can be created. Without the need for a biasing field, the design and implementation of skyrmion based devices are significantly simplified. The small size of the skyrmions, combined with the incredible stability generated here, could be potentially useful for the design of next-generation spintronic devices that are energy efficient and can outperform current memory technologies.” To further the development of skyrmion based electronics, the team is currently looking at how nanoscale skyrmions interact with each other and with electrical currents.

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