Spin Hall Effect

Researchers at Japan's Tokyo Institute of Technology (Tokyo Tech) have demonstrate the concept of Berry phase monopole engineering of the spin Hall effect in non-centrosymmetric silicide TaSi₂.

Image credit: Tokyo Tech

Spin-transfer torque is an important phenomenon that enables ultrafast and low-power spintronic devices. Recently, however, spin-orbit torque (SOT) has emerged as a promising alternative to spin-transfer torque. Many studies have investigated the origin of SOT, showing that in non-magnetic materials, a phenomenon called the spin Hall effect (SHE) is key to achieving SOT. In these materials, the existence of a “Dirac band” structure, a specific arrangement of electrons in terms of their energy, is important to achieving large SHE. This is because the Dirac band structure contains “hot spots” for the Berry phase, a quantum phase factor responsible for the intrinsic SHE. Thus, materials with suitable Berry phase hot spots are key to engineering the SHE.

Researchers from The Ohio State University in the U.S, Uppsala University in Sweden and the UK's University of Exeter have used a novel technique to confirm a previously undetected physics phenomenon that could be used to improve data storage in the next generation of computer devices.

Spintronic memories, like those used in some high-tech computers and satellites, use magnetic states generated by an electron's intrinsic angular momentum to store and read information. Depending on its physical motion, an electron's spin produces a magnetic current. Known as the "spin Hall effect," this has key applications for magnetic materials across many different fields, ranging from low power electronics to fundamental quantum mechanics.

Researchers at Tokyo Institute of Technology, the University of Tokyo, Japan Science and Technology Agency (JST), RIKEN and Comprehensive Research Organization for Science and Society (CROSS) have demonstrated a large, unconventional anomalous Hall resistance in a new magnetic semiconductor in the absence of large-scale magnetic ordering.

This validates a recent theoretical prediction and provides new insights into the anomalous Hall effect, a quantum phenomenon that has previously been associated with long-range magnetic order.

An international collaboration, led by RMIT, has quantified spin in a 2D quantum spin Hall insulator (QSHI) WTe₂, a promising option for future low-energy nano-electronic and spintronic devices.

Using anisotropic magnetoresistance (AMR) to reveal the relationship between electrons’ spin and momentum, the team demonstrated the promising potential of QSHI for novel spintronic devices, and proved the value of AMR for design and development of QSHI-based spintronics.

Researchers from MIT discovered that under a powerful magnetic field and at very low temperatures, graphene can filter electrons according to the direction of their spin. This is something that cannot be done by any conventional electronic system - and may make graphene very useful for quantum computing.

it is known that when a magnetic field is turned on perpendicular to a graphene flake, current flows only along the edge, and in one direction (clockwise or counterclockwise, depending on the magnetic field orientation), while the bulk graphene sheet remains insulating. This is called the Quantum Hall effect.

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.

Durham University spun-off a new company called Rhomap to develop manufacture-to-order scientific instrumentation for high precision magneto-transport measurement systems. Rhomap's instruments targets new materials and next generation semiconductors, photovoltaics, spintronics and ferromagnetic systems.

The new Ohmpoint Measurement System is a flexible research tool that offers a range of software selectable sample connection probe geometries in one system. The instrument allows users to measure resistance in two or four point geometry, sheet resistance and magneto-transport behavior, including Hall effect and magnetoresistance. The flexibility of the system also enables the user to easily select between individual measurements and batch scanning of multiple samples.

Plures Technologies announced that it will merge with CMSF Corporation, a publicly traded company with no significant operations. This means that the Plures will become a public company (OTCBB:CMSF). The public company will be called Plures Technologies. Plures main business it its 95% stake in Advanced MicroSensors Corporation (AMS). AMS is a semiconductor foundry, which develops and fabricates MEMS and spintronics solutions.

AMS's magnetic sensor product line uses magnetoresistive (AMR, GMR) materials and magnetic tunnel junctions (MTJs). According to the company, their sensors exhibit excellent performance, and they outperform traditional Hall Effect devices with regard to size, power, sensitivity, accuracy and resolution.

There's a free discussion meeting in London, UK, about Spintronics. It will take place at 28-29  September 2009, at The Royal Society, London. Here's what the organizers say:

Recent advances in generating, manipulating and detecting spin-polarized electrons promise entirely new classes of spin based sensor, memory and logic devices, generally referred to as the field of spintronics.

Physicists in the US are the first to detect the spin Hall effect at room temperature, in what could be an important development in the quest for a practical source of spin-polarized electrons for spintronic devices.

David Awschalom and colleagues at the Center for Spintronics and Computation at the University of California, Santa Barbara observed the current-induced spin-polarization of electrons and the spin Hall effect in thin surface layers of ZnSe.

The 'spin Hall' is a spin current flowing in a transverse direction to the charge current in a non-magnetic material and in the absence of an applied magnetic field. The result is a measurable accumulation of “spin up” and “spin down” electrons at opposite edges of the conducting channel. 

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