Spintronics - Page 4

Graphene Flagship Partners RWTH Aachen University and AMO GmbH, both based in Germany, recently launched a new joint research center with a focus on efficiently bridging the gap between fundamental science and applications within graphene and related materials based electronics and photonics.

The five founding Principal Investigators of the Aachen Graphene & 2D-Materials Center are all members of the Graphene Flagship and share the vision of bringing graphene and related materials research from the lab into applications. The Center will help to turn the exciting properties of graphene and 2D-materials into true functions, making these materials not only fascinating for scientists but also serving society, as was explained.

Researchers at Chalmers University, affiliated with the Graphene Flagship, have devised a graphene-based spin field-effect transistor with the ability to function at room temperature. The team used the spin of electrons in graphene and similar layered material heterostructures to fabricate working devices in a step towards combining memory devices and the logic of spintronics.

The researchers demonstrated that the spin characteristics of graphene can be electrically regulated in a controlled way, even at an ambient temperature. In addition to possibly unlocking various probabilities in spin logic operations, this study also enables integration with magnetic memory elements in a device unit. If further advancements can assist in the production of a spin current without the need for charge flow, the amount of power needed will be considerably reduced, resulting in highly versatile devices.

NUS researchers discovered that manipulating the electron spin lowers the contact resistance in graphene-metal interfaces, which normally suffer from large electrical resistance.

The researchers have shown that edga-contacted device geometries in metallic-graphene interfaces feature some of the lowest contact resistances reported to date - significantly lower than in surface-contracted interfaces. The researchers explain that this is due to the different behavior of electron spins in these geometries.

Researchers from Grenoble Alpes University in France have demonstrated (using atomistic calculations) that a lateral electric field can be used to tune the carrier mobility and change the spin polarization of the current driving through zigzag graphene ribbons.

The calculations predict a high variation of the carrier mobility, mean free path and spin polarization in the ZGNRs. It turns out that configurations with almost 100% spin-polarized current can be switched on and off. The researchers say that these effects can be nicely exploited in spintronics devices.

Researchers at Pennsylvania State University have developed a device made of bilayer graphene, which provides experimental proof of the ability to control the momentum of electrons. The study is considered as a step forward in a new field of physics called valleytronics.

The team explains that current silicon-based transistor devices rely on the charge of electrons to turn the device on or off, but valleytronics looks into a new way to manipulate electrons based on other variables, called degrees of freedom. Charge is one degree of freedom. Electron spin is another, and the ability to build transistors based on spin, called spintronics, is still in the development stage. A third electronic degree of freedom is the valley state of electrons, which is based on their energy in relation to their momentum.

Saint Jean Carbon, a carbon science company engaged in the exploration of natural graphite properties and related carbon products, has teamed up with the University of Western Ontario to create graphene that has a magnetic field (Magnetoresistance).

One of the involved researchers explained that: "Magnetoresistance (MR) refers to the significant change of electrical resistance of materials under a magnetic field. Magnetoresistance effects have been applied in magnetic sensors, spintronic devices and data storage. Magnetic sensors are extremely useful for today's industry for measurement and control purposes... This happens by detecting changes in electrical resistance brought on by the presence of a magnetic field. This is also known as magnetoresistance (MR). The market size of the magnetic sensor is increasing with annual growth rate at 10% because of new nanomaterials..."

A team of researchers from China and Japan has designed a new method to make minuscule ribbons of graphene that are highly sought-after building blocks for semiconductor devices thanks to their predicted electronic properties. These structures, however, have proven challenging to make.

Previous attempts at making graphene nanoribbons relied on placing sheets of graphene over a layer of silica and using atomic hydrogen to etch strips with zigzag edges, a process known as anisotropic etching. This method, however, only worked well to make ribbons that had two or more graphene layers. Irregularities in silica created by electronic peaks and valleys roughen its surface, so creating precise zigzag edges on graphene monolayers was a challenge.

A team of scientists at the U.S. Naval Research Laboratory (NRL) has demonstrated hyperthermal ion implantation (HyTII) as an effective means of doping graphene with nitrogen atoms. The result is a low-defect film with a tunable bandstructure that could be useful in a variety of device platforms and applications.

According to the research, the HyTII method delivers a high degree of control including doping concentration and, for the first time, demonstrates depth control of implantation by doping a single monolayer of graphene in a bilayer graphene stack. This further demonstrates that the resulting films have high-quality electronic transport properties that can be described solely by changes in bandstructure rather than the defect-dominated behavior of graphene films doped or functionalized using other methods.

The Graphene Flagship includes a Spintronics Work Package - the aims to explore graphene's role in spintronics. Last week the participants in this initiative met for the first time in an event organised by the Deputy Leader of the Spintronics Work Package, and hopefully these interesting projects will bear fruit soon.

• HiMagGraphene: Atomic-scale control of graphene magnetism using hydrogen atoms
• iSpinText: Induced Spin Textures in van der Waals Heterostructures
• SOgraph: Tailoring Spin-Orbit effects in Graphene for spin-orbitronic applications
• TAILSPIN: Tailoring spin-interactions in graphene nanoribbons for ballistic fully spin-polarized devices
• Trans2DTMD: Theoretical investigation of electronic transport in functionalized 2D transition metal dichalcogenides

Researchers at the Autonomous University of Madrid, in collaboration with CIC nanoGUNE and the Institut Néel of Grenoble, have demonstrated that the simple absorption of a hydrogen atom on a layer of graphene magnetizes a large region of it. As a result, by selectively manipulating these hydrogen atoms, it is possible to produce magnetic graphene with atomic precision.

Graphene inherently lacks magnetic properties. The hydrogen atom has the smallest magnetic moment (the magnitude that determines how much and in what direction a magnet will exert force). This work reveals how when a hydrogen atom touches a graphene layer it transfers its magnetic moment to it. The researchers explain that in contraposition to more common magnetic materials such as iron, nickel or cobalt, in which the magnetic moment generated by each atom is located within a few tenths of a nanometre, the magnetic moment induced in the graphene by each atom of hydrogen extends several nanometres, and likewise displays a modulation on an atomic scale.