Graphene - Page 3

Researchers at CIC nanoGUNE BRTA in Spain and University of Regensburg in Germany have recently demonstrated spin precession at room temperature in the absence of a magnetic field in bilayer graphene. In their paper, the team used 2D materials to realize a spin field-effect transistor.

Sketch of the spin field-effect transistor. Image from article

Coherently manipulating electron spins at room temperature using electrical current is a major goal in spintronics research. This is particularly valuable as it would enable the development of numerous devices, including spin field-effect transistors. In experiments using conventional materials, engineers and physicists have so far only observed coherent spin precession in the ballistic regime and at very low temperatures. Two-dimensional (2D materials), however, have unique characteristics that could provide new control knobs to manipulate spin procession.

Two recent studies by a collaborative team of scientists from two NCCR MARVEL labs have identified a new type of defect as the most common source of disorder in on-surface synthesized graphene nanoribbons (GNRs).

Combining scanning probe microscopy with first-principles calculations allowed the researchers to identify the atomic structure of these so-called "bite" defects and to investigate their effect on quantum electronic transport in two different types of graphene nanoribbon. They also established guidelines for minimizing the detrimental impact of these defects on electronic transport and proposed defective zigzag-edged nanoribbons as suitable platforms for certain applications in spintronics.

A team of researchers from The University of Groningen and Columbia University have found that 2D spin-logic devices could benefit from magnetic graphene that can efficiently convert charge to spin current, and can transfer this spin-polarization over long distances.

Graphene is known amongst 2D materials for transporting spin information, but cannot generate spin current unless its properties are modified – conventionally cobalt ferromagnetic electrodes are used for injecting and detecting the spin signal.

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. This achievement may, according to the researchers, push forward the spintronics field.

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.

University of Groningen researchers have measured the presence of electron-spin-dependent nonlinearity in a van der Waals heterostructure spintronic device. The team went on to demonstrate its application for basic analog operations such as essential elements of amplitude modulation and frequency sum (heterodyne detection) on pure spin signals, by exploiting the second-harmonic generation of the spin signal due to nonlinear spin injection.

Graphene (light green) with boron nitride (blue) on top. Measuring points indicated in orange.

The researchers also showed that the presence of nonlinearity in the spin signal has an amplifying effect on the energy-dependent conductivity-induced nonlinear spin-to-charge conversion effect. The interaction of the two spin-dependent nonlinear effects in the spin-transport channel leads to a highly efficient modulation of the spin-to-charge conversion effect, which in principle can also be measured without using a ferromagnetic detector. These effects are measured both at room and low temperatures, and are suitable for their applications as nonlinear circuit elements in the fields of advanced spintronics and spin-based neuromorphic computing.

The european Graphene Flagship project has announced 16 newly-funded graphene FLAG-ERA projects. These projects which will become Partnering Projects of the Graphene Flagship – receiving around €11 million in funding overall.

Two of these projects will investigate the promising properties of graphene for spintronics. The SOgraphMEM project will test specific materials for a novel branch of spintronics called spin-orbitronics, while the DIMAG project will fabricate new layered magnetic materials with optimal characteristics for spintronics applications.

Researchers from the Korea Advanced Institute of Science and Technology (KAIST) have developed a new method to apply graphene as an active spintronic component for generating, controlling, and detecting spin current without ferromagnetic electrodes or magnetic fields.

The KAIST researchers observed highly efficient charge-to-spin interconversion via the gate-tunable Rashba-Edelstien effect (REE) in graphene heterostructures. The researchers used graphene stacked on top of a large spin-orbit coupling transition metal dichalcogenide material (2H-TaS₂).

Researchers from Spain's ICN2 institute have used numerical simulations to show that spin diffusion length in graphene is independent of grain size. The researchers base their calculations on CVD grown graphene. CVD methods produces high quality materials that are built from several single-crystal sheets separated from one another through grain boundaries.

The research have shown that the grain boundaries do not have any effect on the spin transport. The researchers considered two different mechanisms for spin relaxation - randomization of spins within the grains due to spin-orbit coupling, and scattering in a grain boundary. The main implication of this research is that single-domain graphene may not be a requirement for spintronics applications.

The International Institute of Physics in Brazil recently uploaded this interesting talk by Ahmet Avsar, from the EPFL, who discusses spintronics in 2D materials (such as graphene):

This talk was given as part of the IIP's 2D Materials: From Fundamentals to Spintronics workshop which took place in early October.

Researchers from the University of Groningen developed a two-dimensional spin transistor, in which spin currents were generated by an electric current through graphene. The device also include a monolayer transition metal dichalcogenide (TMD) that is placed on the graphene to induce charge-to-spin conversion.

Graphene is an excellent spin transporter, but spin-orbit coupling is required to create or manipulate spins. The interaction is weak in the graphene carbon atoms, but now the researchers have shown that adding the TMD layer increases the spin-orbit coupling.