Spin current - Page 6

Researchers from Japan's Kyoto University and Osaka University have demonstrated that spin currents can travel more than half a micrometer on a thin doped-germanium sheet. Up until now this has only been demonstrated in very low temperatures (below 225 Kelvin).

Germanium has a higher electron mobility than silicon and a particular lattice symmetry that should reduce much of the electrons spin relaxation. But the material is not magnetic and so measuring spin transport is not easy because spin currents have to be created in a magnetic material and injected into germanium.

Researchers from Tohoku University and the Japan Science and Technology Agency (JST) have confirmed that surface plasmon resonance can be used to generate spin currents.

Surface plasmon resonance happens when electrons are hit by photos and react by vibrating. It is commonly used in bio-sensors and lab-on-a-chop systems. The researchers have shown that directing light on a certain magnetic material, a spin current can be produced and controlled.

Researchers from the US Naval Research Laboratory (NRL) developed a new type of tunnel device structure in which both the tunnel barrier and transport channel are made from graphene. The researchers say that this device features the highest spin injection values yet measured for graphene, and this design could pave they way towards highly functional and scalable graphene electronic and spintronic devices.

The tunnel barrier is made from dilutely fluorinated graphene while the charge and transport layer is made from graphene. The researcher demonstrated tunnel injection through the fluorinated graphene, and lateral transport and electrical detection of pure spin current in the graphene channel.

Researchers from Tohoku Univeristy generated a new kind of magnetoresistance in a system with an insulating magnet. They call this new phenomenon Spin Hall magnetoresistance (SMR). In SMR, the current does not need to pass through a magnet. The researchers developed a system in which a normal metal is put in contact with a magnetic insulator. The resistance of the normal metal is influenced by the magnetization in the insulating magnet even though none of the charge current is able to pass through the magnet.

The SMR effect is a result of spin current being able to flow from the metal into the magnetic insulator. The rate of this spin transfer depends on the magnetization direction of the insulator. The more spin current passing across the metal-insulator interface, the weaker the charge current flowing through the metal.

Researchers from the University of Delaware confirmed that electrons generate a magnetic field. In materials made from two layers of a heavy metal and a ferromagnetic material, the spin current diffuses into the ferromagnetic material. When this happens, a magnetic field is generated.

This magnetic field does not radiate beyond the ferromagnetic material (unlike regular magnetic fields). This is important in applications such as MRAM in which shielding the magnetic fields between memory cells is difficult. If devices use the new magnetic field it may be easier to create high density MRAM cells or other devices.

Theoretical research by A*STAR researchers in Singapore shows that spin-polarized current can simply be achieved by applying an oscillating voltage across the device. Spin-polarized is critical for Spintronics devices, but imperfections in a material can easily destroy the polarization.

The researchers looked at a two-dimensional electron gas (in which the electrons can move only in one plane). If you pass a spin-polarized current through this gas, a Rashba spin-orbit coupling effect makes the spin change (first upwards and then downwards) - which reduces the polarization to zero. Using a spin-current rectifier (like a spin polarization filter) one can control the strength of the Rashba coupling effect and so prolong the spin current's polarization life.

Researchers from the Japanese RIKEN institute have shown that spin information in some materials can travel much further than previously thought. The researchers managed to measure the spin diffusion in detail by using two magnetic contacts to inject the spin signal into a thin silver wire. This enhances the amount of spin polarization present in the wire. Using a third contact that picks the signals, they were manage to manage the polarization degree at several distances along the wire.

They say that spin current was detected at distances of over ten micrometers. The absolute magnitude of the spin signal decreases with travel distance, but the quality of the spin precession signal (coherence) is actually improved - due to the fact that the collective coherent precession of the spins has a beneficial effect on the overall spin polarization over time.

Researchers from Cambridge University developed a more efficient way to generate spin current, using the collective motion of spins called spin waves (the wave property of spins). There are a number of different interactions in spin waves and the researchers's idea was to use such spin wave interactions for generating efficient spin currents.

One of the spin wave interactions (called three-magnon splitting) generates spin current 10 times more efficiently than using pre-interacting spin-waves.

Researchers from the City University of Hong Kong managed to generate a spin current in Graphene, which could 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.

Researchers from the Hitachi Cambridge Laboratory in the University of Cambridge developed a new technology that enables the control (and detection) of spin current. The idea is to use laser light to sustain the spin signal during transit and to manipulate it by applying a voltage. The detection is done electrically.

The team admits that for high-volume information processing this will not really be practical, but this method proves the spin-transistor principle and it be lay the ground work for next-generation devices.