Ultrafast all-optical spin injection in silicon revealed at FERMI

A revolutionary and energy-efficient information technology encoding digital data in electron spin (spintronics) by combining semiconductors and ferromagnets is being developed worldwide. Merging of memory and logic computing of magnetic based storage devices and silicon-based logic transistors is expected to ultimately lead to new computing paradigms and novel spin-based multifunctional devices. The advantages of this new technology would be non-volatility, increased data processing speed, reduced electric power consumption. All of them are essential steps towards next generation quantum computers.

To create spin-based electronics with potential to revolutionize information technology, silicon, the predominant semiconductor, needs to be integrated with spin functionality. Although silicon is non-magnetic at equilibrium, spin polarized currents can be established in Si by a variety of approaches such as the use of polarized light, hot electrons spin injection, tunnel spin injection, Seebeck spin tunneling and dynamical spin pumping methods, as had been demonstrated recently. In general, spin polarized currents refer to the preferential alignment of the spin angular momentum of the electrons in a particular direction.

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Image: Figure 1: a) the optical generation of spin polarized superdiffusive currents across a ferromagnetic/semiconductor interface is illustrated. b) the principles of TR-MOKE experiment are illustrated  together with a cross-section TEM image describing the quality of the Ni/Si interface.

Antiferromagnets as a new kind of information storage technology

Magnetic materials have been used for storing information for more than half a century, from the first magnetic tapes to modern data servers. These technologies have in common the usage of ferromagnets, producing magnetic fields which are easily measurable. Researchers at the University of Nottingham are working with Diamond Light Source to develop new technologies based on a different class of magnetic material: an antiferromagnet, which does not produce a magnetic field, but which has a hidden magnetic order that can be used to store the ones and zeros of information.

Looking at the atomic scale, each atom is like a small magnetic compass, having a small magnetic moment. In a ferromagnet, once the information is written, all those atomic moments remain oriented in the same direction. In antiferromagnets, each magnetic moment aligns exactly opposite to its neighbours, effectively cancelling them out (Figure 1). This arrangement has some important advantages for memory applications: magnetic bits do not interact with each other, so can be packed more closely; they do not interact with external magnetic fields; their resonant frequencies, which determine the speed that information can be written, is typically 1000 times larger than in ferromagnets. Antiferromagnets can therefore be useful, but how would you store and read information in a material whose total magnetic moment is always zero? Dr Peter Wadley, a researcher at the University of Nottingham, and Sonka Reimers, a joint Nottingham and Diamond PhD student, are trying to answer that question in their search for new technologies for information storage and processing.

>Read more on the Diamond Light Source website

Figure: Schematic of magnetic moment orientation for binary information storage using (left) a ferromagnet. Full image here.

X-Rays Reveal ‘Handedness’ in Swirling Electric Vortices

Scientists at Berkeley Lab study exotic material’s properties, which could make possible a new form of data storage

Scientists used spiraling X-rays at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) to observe, for the first time, a property that gives handedness to swirling electric patterns – dubbed polar vortices – in a synthetically layered material.

Read more on the Berlekely Lab website

Image: This diagram shows the setup for the X-ray experiment that explored chirality, or handedness, in a layered material. The blue and red spirals at upper left show the X-ray light that was used to probe the material. The X-rays scattered off of the layers of the material (arrows at upper right and associated X-ray images at top), allowing researchers to measure chirality in swirling electrical vortices within the material. (Credit: Berkeley Lab)

The miracle material graphene: convex as a chesterfield

Graphene possesses extreme properties and can be utilised in many ways.

Even the spins of graphene can be controlled through use of a trick. This had already been demonstrated by a HZB team some time ago: the physicists applied a layer of graphene onto a nickel substrate and introduced atoms of gold in between (intercalation).

The scientists now show why this has such a dramatic influence on the spins in a paper published in 2D Materials. As a result, graphene can also be considered as a material for future information technologies that are based on processing spins as units of information.

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