Researchers discover that pure-spin current is possible in insulators

Researchers from the US DoE's Argonne National Laboratory discovered that a pure-spin current can be created in materials that are insulators. Previously it was thought that such a current is possible in magnetic materials only.

SSE in Paramagnets image

The researchers generated a magnetic field on a layer of ferromagnetic YIG (yttrium iron garnet) on a substrate of paramagnetic GGG (gadolinium gallium garnet). To their surprise, the spin current was stronger in the GGG than it was in the YIG. They actually do not know how this works - and understanding it is the next step in their research.

New room-temperature tunnel device developed using graphene as tunnel barrier and transport channel

Researchers from the U.S. Naval Research Laboratory (NRL) developed a new type of room-temperature tunnel device structure in which the tunnel barrier and transport channel are both made of graphene.

NRL scientists use graphene as tunnel barrier for spintronics image

In this new design, hydrogenated graphene acts as a tunnel barrier on another layer of graphene for charge and spin transport. The researchers demonstrated spin-polarized tunnel injection through the hydrogenated graphene, and lateral transport, precession and electrical detection of pure spin current in the graphene channel. The team sasy that the spin polarization values are higher than those found using more common oxide tunnel barriers, and spin transport at room temperature.

Spin current shown to travel over half a micrometer in a thin doped germanium film

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).

Spin-transport in room-temperature germanium image

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 show that plasmon resonance can be useful for spintronics applications

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.

Tohoku JST plasmon resonance for spintronics

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.

NRL scientists report the highest spin injection values yet measured for graphene

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.

Spin Hall magnetoresistance discovered using an insulating magnet

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.

Spin Hall magnetoresistance image

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.

Researcher confirm the existence of electron-generated magnetic fields

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.

Spin-polarized currents sustained using an oscillating voltage

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.

Spin information can travel much further than thought before

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.

Using spin waves can efficiently generate spin current

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.