Spintronics - Page 7

Researchers from the University of British Columbia have discovered that magnetic defects may be behind graphene's slow the spin-relaxation time (which is as much as 1000 times lower in graphene than predicted).

The researchers applied a voltage between two metal contracts on a graphene sheet that was 12x4 micrometers in size, while changing the strength of a magnetic field piercing the strip. The small sized sheet was chosen because interference effects cause the current to fluctuate rapidly with the magnetic field. They analyzed those fluctuations and concluded that the primary source of electron spin relaxation is magnetic defects—and not, as researchers have previously assumed, the spin-orbit effect.

Researchers from Germany, Russia and the USA managed to increase graphene's conduction electrons' spin-orbit coupling by a factor of 10,000. They say this could enable a Spintronics switch that is controlled by a small electric field. To develop this, the researchers placed graphene on a nickel substrate in which atoms are separated by the same distance as the graphene's hexagonal meshes. They then deposited gold atoms on the device which ended up between the graphene and nickel sheets.

The electrons in the graphene layer exhibited an increased spin-orbit coupling - in fact 10,000 stronger compared to a regular graphene sheet. They say that such a strong spin-orbit coupling could be used to develop a Spintronics switch - in which the spin can be rotated using an electric field. The switch will include two perpendicular spin filters that will be controlled by the electric field.

Researchers from the US Naval Research Laboratory (NRL) discovered a way to use graphene as an extremely thin "tunnel barrier" to conduction. This could be very useful for Spintronics devices. The researchers have shown that graphene can serve as an excellent tunnel barrier when current is directed perpendicular to the plane of carbon atoms. The spin polarization of the current is also preserved by the tunnel barrier.

The researchers replaced the normally used oxide barriers (which introduce defects into the system and feature too high a resistance) with graphene - which is defect resistant and chemically inert and stable.

Researchers from Georgia State University (GSU) and the Georgia Institute of Technology (Georgia Tech) developed a new technique to study the spin characteristics of electrons in graphene, which could move us closed to graphene-based Spintronics devices.

The research team detected spin-resonance using electrical resistance, by illuminating the device by microwaves (which causes the spin-splitting energy to equalize). The device’s resistance is altered when the microwave energy is absorbed by the device. This effect is small and difficult to measure normally, but by using Graphene, enabled them to actually witness this effect.

Researchers from the University of South Florida and the University of Kentucky managed to create a material the spin of the electrons can be set in a controlled manner. The team suggest using cobalt atoms on a graphene sheet.

The researchers have used state-of-the-art theoretical computations to prove this, they haven't actually made the material and controlled the spin.

Researchers from China's Fudan University say that graphene nanoribbons could potentially be used to create spin valves (one of the basic building blocks of spintronics). They present a theoretic spin valve design that uses two hexagonal graphene "nanoislands" with zig-zag edges, which serve as the magnetic layers in the spin valve, connected by an armchair-type nanoribbon as the non-magnetic layer, through which the electrons can pass depending on the relative alignment of the spins in the nanoislands.

They calcualte that this design enables stable spin configurations at certain energies, and there will be stable configurations in which the islands are polarized either parallel or antiparallel with respect to each other — a necessary requirement for a spin valve.

The National Science Foundation (NSF) granted a four-year $1.85 million research project to UC Riverside researchers - to develop spin-based memory and logic chip. The researchers are working towards a magnetologic gate that will serve as the engine for the new technology - similar to the role of the transistor in conventional electronics.

The magnetic gate consists of graphene contacted by several magnetic electrodes. Data is stored in the magnetic state of the electrodes, similar to the way data is stored in a magnetic hard drive. For the logic operations, electrons move through the graphene and use its spin state to compare the information held in the individual magnetic electrodes.

Graphene can adsorb oxygen onto its surface (which changes graphene's electronic transport properties). This can be useful for Spintronics devices, but the adsorption is difficult to control. Researchers from the Tokyo Institute of Technology developed a way to control the adsorption of oxygen by applying an electric field to a Graphene-based field-effect transistor (FET).

The density of carriers (electrons and holes) in the FET can be tuned by applying an electric field to the gate of the device and, when oxygen molecules then adsorb onto the device, the conductivity of the FET changes.

Researchers from Europe developed a graphene-based device that can detect magnetic fields with a record sensitivity (down to the stray field of few magnetic molecules, better than the previous record of sensitivity by a factor of 100). The graphene was used like a spider web to chemically 'trap' the molecules and detect their magnetization at the same time. This new development may enable ultra-high density Spintronics memory and molecular sensors.

This device was built by depositing magnetic molecules on a graphene sheet. The molecules were synthesized so that they are suitable to graft the graphene lattice. The electrical measurements were performed at very low temperature (to limit the noise). The new device works pretty much like a spin valve, only it's much smaller.

Researchers from the City University of Hong Kong managed to generate a spin current in Graphene. This can lead us to using Graphene as a spintronics device.

The scientists used spin splitting in monolayer graphene generated by ferromagnetic proximity effect and adiabatic (a process that is slow compared to the speed of the electrons in the device) quantum pumping. They can control the degree of polarization of the spin current by varying the Fermi energy (the level in the distribution of electron energies in a solid at which a quantum state is equally likely to be occupied or empty), which they say is very important for meeting various application requirements.