Magnetism - Page 2

Researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have developed a method to stabilize the edges of graphene nanoribbons and directly measure their unique magnetic properties.

The team, co-led by Felix Fischer and Steven Louie from Berkeley Lab’s Materials Sciences Division, found that by substituting some of the carbon atoms along the ribbon’s zigzag edges with nitrogen atoms, they could discretely tune the local electronic structure without disrupting the magnetic properties. This subtle structural change further enabled the development of a scanning probe microscopy technique for measuring the material’s local magnetism at the atomic scale.

Researchers from Spain, Finland and France have demonstrated that magnetism and superconductivity can coexist in graphene, opening a path towards graphene-based topological qubits.

Schematic illustration of the interplay of magnetism and superconductivity in a graphene grain boundary, a potential building block for carbon-based topological qubits Credit: Jose Lado/Aalto University

In the quantum realm, electrons can behave in interesting ways. Magnetism is one of these behaviors that can be seen in everyday life, as is the rarer phenomena of superconductivity. Intriguingly, these two behaviors are often antagonists - the existence of one of them often destroys the other. However, if these two opposite quantum states are forced to coexist artificially, an elusive state called a topological superconductor appears, which is useful for researchers trying to make topological qubits.

An international research team, led by the University at Buffalo, has reported an advancement that could help give graphene magnetic properties. The researchers describe in their work how they paired a magnet with graphene, and induced what they describe as artificial magnetic texture in the nonmagnetic material.

The image shows eight electrodes around a 20-nanometer-thick magnet (white rectangle) and graphene (white dotted line). Credit: University at Buffalo.

Independent of each other, graphene and spintronics each possess incredible potential to fundamentally change many aspects of business and society. But if you can blend the two together, the synergistic effects are likely to be something this world hasn’t yet seen, says lead author Nargess Arabchigavkani, who performed the research as a PhD candidate at UB and is now a postdoctoral research associate at SUNY Polytechnic Institute.

Researchers at the University of Basel in Switzerland, Budapest University of Technology and Economics in Hungary and National Institute for Material Science in Japan have developed a new, super-small device that is capable of detecting minute magnetic fields.

A conventional SQUID (left) and the new SQUID (right). (University of Basel, Department of Physics)

The device, a new kind of superconducting quantum interference device (SQUID), is just 10 nanometres high, or around a thousandth of the thickness of a human hair. It's made from two layers of graphene making it one of the smallest SQUIDs ever built separated by a very thin layer of boron nitride.

A collaborative group of scientists has designed a device that makes use of graphene’s assorted talents: superconducting, insulating, and a type of magnetism called ferromagnetism. The multitasking device could enable new physics experiments, such as research in the pursuit of an electric circuit for faster, next-generation electronics like quantum computing technologies.

An optical image of the graphene device (shown above as a square gold pad) on a silicon dioxide/silicon chip. Shining metal wires are connected to gold electrodes for electrical measurement. (Credit: Guorui Chen/Berkeley Lab)

So far, materials simultaneously showing superconducting, insulating, and magnetic properties have been very rare. And most people believed that it would be difficult to induce magnetism in graphene, because it’s typically not magnetic. Our graphene system is the first to combine all three properties in a single sample, said Guorui Chen, a postdoctoral researcher in Wang’s Ultrafast Nano-Optics Group at UC Berkeley, and the study’s lead author.

Stanford physicists recently observed a novel form of magnetism, predicted but never seen before, that is generated when two graphene sheets are carefully stacked and rotated to a special angle. The researchers suggest the magnetism, called orbital ferromagnetism, could prove useful for certain applications, such as quantum computing.

Optical micrograph of the assembled stacked structure, which consists of two graphene sheets sandwiched between two protective layers made of hexagonal boron nitride. (Image: Aaron Sharpe)

We were not aiming for magnetism. We found what may be the most exciting thing in my career to date through partially targeted and partially accidental exploration, said study leader David Goldhaber-Gordon, a professor of physics at Stanford’s School of Humanities and Sciences. Our discovery shows that the most interesting things turn out to be surprises sometimes.

Researchers from the University of Geneva (UNIGE) in Switzerland and the University of Manchester in the UK have found an efficient way to control infrared and terahertz waves using graphene. "There exist a class of the so-called Dirac materials, where the electrons behave as if they do not have a mass, similar to light particles, the photons," explains Alexey Kuzmenko, a researcher at the Department of Quantum Matter Physics in UNIGE's Science Faculty, who co-conducted this research together with Ievgeniia Nedoliuk.

The interaction between graphene and light suggests that this material could be used to control infrared and terahertz waves. "That would be a huge step forward for optoelectronics, security, telecommunications and medical diagnostics," points out the Switzerland-based researcher.

Researchers from IMDEA Nanociencia and other European centers have discovered that the combination of graphene with cobalt offers relevant properties in the field of magnetism. This breakthrough sets the stage for the development of new logic devices that can store large data amounts quickly and with reduced energy consumption.

One of the latest technologies for digitally encoding information is spin orbitronics, which not only exploits the charge of the electron (electronics) and its spin (spintronics), but also the interaction of the spin with its orbital motion, offering a multitude of properties.

A study by Brazilian physicist Aline Ramires with Jose Lado, a Spanish-born researcher at the Swiss Federal Institute of Technology (ETH Zurich), showed that a simple sheet of graphene has fascinating properties due to a quantum phenomenon in its electron structure called Dirac cones. The system becomes even more interesting if it comprises two superimposed graphene sheets, and one is very slightly turned in its own plane so that the holes in the two carbon lattices no longer completely coincide. For specific angles of twist, the bilayer graphene system displays exotic properties such as superconductivity.

The researchers found that the application of an electrical field to such a system produces an effect identical to that of an extremely intense magnetic field applied to two aligned graphene sheets. "I performed the analysis, and it was computationally verified by Lado," Ramires said. "It enables graphene's electronic properties to be controlled by means of electrical fields, generating artificial but effective magnetic fields with far greater magnitudes than those of the real magnetic fields that can be applied."

Researchers from the Regional Center of Advanced Technologies and Materials (RCPTM) at Palacký University in the Czech Republic, together with the colleagues from the Institute of Physics (FZU) of the Czech Academy of Science (CAS) and the Institute of Organic Chemistry and Biochemistry (IOCB) of the CAS, have designed a new way to control the electronic and magnetic properties of molecules.

Traditionally, such a change can be induced by application of external stimuli, such as light, temperature, pressure, and magnetic field. The Czech scientists have instead developed a way to use weak non-covalent interactions of molecules with the surface of chemically modified graphene.