Room Temperature - Page 4

Electron spin-splitting effect (Rashba effect) was demonstrated in a semiconductor (Bismuth selenide) that is far larger than has ever been seen before. This could lead the way towards room-temperature spintronic devices. The Rashba effect is the phenomenon of spin splitting with an applied electric field instead of a magnetic field.

The Rashba effect is crucial for spintronic devices: for example when designing spin transistors, electrons of a single spin are injected and then – under an applied electric field – have their spins rotated. Rashba effect in well-established semiconductors (silicon or gallium arsenide for example) is very small - and so electrons have to travel large distances before any spin rotation is noticeable. This requires very pure materials and very low temperatures.

Researchers from the University of California, Santa Barbara and the University of Konstanz in Germany, led by David Awschalom reported a breakthrough in the use of diamond in quantum physics. The physicists were able to coax the fragile quantum information contained within a single electron in diamond to move into an adjacent single nitrogen nucleus, and then back again using on-chip wiring.

The discovery shows the high-fidelity operation of a quantum mechanical gate at the atomic level, enabling the transfer of full quantum information to and from one electron spin and a single nuclear spin at room temperature. The process is scalable, and opens the door to new solid-state quantum device development.

Researchers from Japan discovered that dilute ferromagnetic oxide materials remain in a ferromagnetic state at room temperature. The team used cobalt-doped titanium dioxide (Co:TiO2) as their study material. This means hat magnetism and conductivity are correlated in thin films of Co:TiO2. Such materials may plan an important role in spintronic devices (MRAM or spin transistors).

Researchers from the University of Utah developed a new spintronic transistor that can be used to align electron spin for a record period of time in silicon chips at room temperature. The research was funded by the National Science Foundation.

The researchers used electricity and magnetic fields to inject "spin polarized carriers" - namely, electrons with their spins aligned either all up or all down - into silicon at room temperature. The new technique was to use magnesium oxide as a "tunnel barrier" to get the aligned electron spins to travel from one nickel-iron electrode through the silicon semiconductor to another nickel-iron electrode. Without the magnesium oxide, the spins would get randomized almost immediately, half up and half down.

Researchers from the Institut Català de Nanotecnologia (ICN), in Barcelona have demonstrated a new device that induces electron spin motion without net electric current. They call this device a 'ratchet', in analogy to a ratchet wrench which provides uniform rotation from oscillatory motion. The Spin Ratchets achieve directed spin transport in one direction, in the presence of an oscillating signal. Most important, this signal could be an oscillatory current that results from environmental charge noise; thus future devices based on this concept could function by gathering energy from the environment.

The ratchet efficiency can be very high - reported results show electron polarizations of the order of 50%, but they could easily exceed 90% with device design improvements. The spin ratchet, which relies on a single electron transistor with a superconducting island and normal metal leads, is able to discriminate the electron spin, one electron at a time. The devices can also function in a “diode” regime that resolves spin with nearly 100% efficacy and, given that they work at the single-electron level, they could be utilized to address fundamental questions of quantum mechanics in the solid state or to help prepare the path for ultrapowerful quantum or spin computers.

Teams from the Johannes Gutenberg University Mainz (JGU) in Germany and Stanford University have uncovered a new quantum state of matter in Heusler compounds which they claim opens up 'previously unimagined usage possibilities'. The scientist from Mainz has shown that many Heusler compounds can behave like topological insulators (TI).

TIs have been studied in the field of solid state and material physics. Characteristic of topological insulators is the fact that the materials are actually insulators or semiconductors, although their surfaces or interfaces are made from metal - but not ordinary metal. Like superconductors, the electrons on the surfaces or interfaces do not interact with their environment - they are in a new quantum state. In contrast with superconductors, topological insulators have two non-interacting currents, one for each spin direction. These two spin currents, which are not affected by defects or impurities in the material, can be employed in the futuristic electronics field of 'spintronics' and for processing information in quantum computers.

Scientists from UCLA say they created a new class of material with magnetic properties in a dilute magnetic semiconductor (DMS) system. By using a type of quantum structure, they've been able to push the ferromagnetism above room temperature. 

Ferromagnetic coupling in DMS systems, the researchers say, could lead to a new breed of magneto-electronic devices that alleviate the problems related to electric currents. The electric field–controlled ferromagnetism reported in this study shows that without passing an electric current, electronic devices could be operated and functioning based on the collective spin behavior of the carriers. This holds great promise for building next-generation nanoscaled integrated chips with much lower power consumption.

Researchers at the University of Twente in the Netherlands have demonstrated the manipulation and detection of spin-polarized electrons in silicon at room temperature (150C warmer than what was previously achieved). 

The team used careful design of the interface where the electrons enter the silicon - the materials must be pure and of a precisely determined thickness in order to preserve the delicate spin polarization. This is an important step towards spintronic-electronics.

Researchers in the University of Washington say that they have been able to train tiny semiconductor crystals, called nanocrystals or quantum dots, to display new magnetic functions at room temperature using light as a trigger.

Silicon-based semiconductor chips incorporate tiny transistors that manipulate electrons based on their charges. Scientists also are working on ways to use electricity to manipulate the electrons' magnetism, referred to as "spin," but are still searching for the breakthrough that will allow "spintronics" to function at room temperature without losing large amounts of the capability they have at frigid temperatures.

The team led by Daniel Gamelin, a UW chemistry professor, has found a way to use photons – tiny light particles – to manipulate the magnetism of semiconductor nanocrystals efficiently, even up to room temperature.

The team used nanocrystals of a cadmium-selenium semiconductor called cadmium selenide, but replaced some nonmagnetic cadmium ions with magnetic manganese ions. The crystals, smaller than 10 nanometers across (a nanometer is one-billionth of a meter), were then suspended in a colloid solution, like droplets of cream suspended in milk.

Beams of photons were used to align all of the manganese ions' spins, creating magnetic fields as much as 500 times more powerful than in the same semiconductor material without manganese. The magnetic effects were strongest at low temperatures, but remained remarkably strong up to room temperature, Gamelin said.

In a second paper published Sunday (Aug. 16) in the online edition of Nature Nanotechnology, Gamelin's group reported related effects in semiconductor nanocrystals made of zinc oxide but also containing small amounts of manganese impurities.

Researchers in France and the US have lowered the current required for spin transfer down to just 120 microamps at room temperature for a device that measures 45 nm across.

Spin transfer is when the spin angular momentum of charge carriers (usually electrons) in a material is transferred from one place to another. In the MRAM industry, Spin Transfer might help to significantly reduce power consumption, but it draws a large current. But the new technique can help with that. 

Stéphane Mangin from Nancy University and colleagues may fabricated 45 nm diameter spin valves based on cobalt-nickel multilayer elements. Because these devices exhibit perpendicular anisotropy, they are thermally stable and require currents as low as 120 microamps for spin transfer switching without any applied magnetic field.