A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 2 1 3 FERROMAGNETIC GRAPHENE Surprising feats of physics can arise by stacking two sheets of the carbon nanomaterial graphene at a particular angle—an arrangement known as “magic-angle” graphene. Now, a research team from Brown University, Providence, R.I., discovered another mechanism to add to graphene’s impressive list. By inducing a phenomenon known as spin-orbit coupling, magic-angle graphene becomes a powerful ferromagnet. Previously, scientists found that when cooled to near absolute zero, magic-angle graphene transforms into a superconductor. “Magnetism and superconductivity are usually at opposite ends of the spectrum in condensed matter physics, and it’s rare for them to appear in the same material platform,” says lead researcher Jia Li. “Yet we’ve shown that we can create magnetism in a system that originally hosts superconductivity.” Li and his team interfaced magic-angle graphene with a block of tungsten diselenide, a material that has strong spin-orbit coupling. Aligning the stack precisely induces spin-orbit coupling in the graphene. The team found that the magnetic properties of magicangle graphene can be controlled with both external magnetic fields and electric fields, which would make this 2D system an ideal candidate for a magnetic memory device with flexible reading and writing options. Another potential application is in quantum computing, the researchers say. An interface between a ferromagnet and a superconductor has been proposed as a potential building block for quantum computers. The problem, however, is that such an interface is difficult to create because magnets are generally destructive to superconductivity. “We are working on using the atomic interface to stabilize superconductivity and ferromagnetism at the same time,” Li says. “The coexistence of these two phenomena is rare in physics, and it will certainly unlock more excitement.” brown.edu. NEUROMORPHIC SPINTRONICS An international team of collaborators from Tohoku University, Japan, and the University of Gothenburg, Sweden, achieved a breakthrough in neuromorphic spintronics resulting in new technology for brain-inspired comNANOTECHNOLOGY When layers of “magic-angle” graphene (bottom) encounter layers of certain transitions metals, it induces a phenomenon called spin-orbit coupling in the graphene layers. Courtesy of Li lab/Brown University. puting. Researchers demonstrated the first integration of a cognitive computing nano-element, the memristor, into another—a spintronic oscillator. Arrays of these memristor-controlled oscillators combine the non-volatile local storage of the memristor function with the microwave frequency computation of the nano-oscillator networks and can closely imitate the non-linear oscillatory neural networks of the human brain. Triangular holes make this material more likely to crack from le to right. Courtesy of N.R. Brodnik et al./Phys. Rev. Lett. In this award-winning image taken with a scanning electron microscope, the green spots are a surface coating developed to limit transmission of SARS-CoV-2. The flower was added. Ph.D. candidate Mohsen Hosseini and chemical engineering professor William Ducker, Virginia Tech, won the “most whimsical” category in the National Nanotechnology Coordinated Infrastructure image contest, held annually in celebration of National Nano Day. vt.edu. BRIEF Contest-winning image titled “Lotus on Anti-SARS-CoV-2 Coating.” Researchers examined the operation of a test device comprising one oscillator and one memristor. Resistance of the memristor changed with the voltage hysteresis applied to the top electrode. Upon voltage application to the electrode, an electric field was applied at the high-resistance state, compared to electric current flows for the low-resistance state. The effects of electric field and current on the oscillator differed from each other, offering various controls of oscillation and synchronization properties. www.tohoku.ac.jp/en, www.gu.se/en. Researchers are making progress on the development of energy-e icient artificial neurons capable of emulating braininspired processes.
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