Spintronics-Info: the spintronics experts

Researchers from the Tokyo Institute of Technology (Tokyo Tech) developed a new MRAM cell structure that relies on unidirectional spin Hall magnetoresistance (USMR). The new cell structure is reportedly very simple with only two layers which could lead to lower-cost MRAM devices.

The spin Hall effect leads to the accumulation of electrons with a certain spin on the lateral sides of a material. By combining a topological insulator with a ferromagnetic semiconductor, the researchers managed to create a device with giant USMR.

As 2019 is coming to an end, it is nice to take a look at the year that passed with its interesting spintronics related research activities and advances.

Here are the top 10 stories posted on Spintronics-Info in 2019, ranked by popularity (i.e. how many people read the story):

1. EU researchers fabricated graphene-based spintronics devices that utilize both electron charge and spin at room temperature (Jan 16)
2. Researchers announce a breakthrough in pinning domain wall propagation (Feb 28)
3. Researchers report on electric field controlled motion in Skyrmions (Mar 15)
4. Researchers develop a way to inject an ultra-fast pulse of spin current (Jan 22)
5. UTSA researchers use reduced graphene oxide to develop efficient spintronics interconnects (Apr 6)
6. Researchers develop a 200Mhz spintronics-based microcontroller unit (Feb 26)
7. HZB researchers managed to switch superferromagnetism with electric-field induced strain (Feb 17)
8. Researchers develop a new technique for ultra-fast teraherz spintronics switching (Mar 12)
9. Optically-assisted MRAM could be a thousand time more efficient then current MRAM devices (May 20)
10. Quantum Well structures can enhance the TMR of MTJs (Sep 25)

Researchers from Kiel University and European colleagues designed and fabricated single molecular spin switches. The newly developed molecules feature stable spin states and do not lose their functionality upon adsorption on surfaces.

The researchers say that the spin states of the new compounds are stable for at least several days. The new molecules have three properties that are coupled with each other in such a feedback loop: their shape (planar or flat), the proximity of two subunits, called coordination (yes or no), and the spin state (high-spin or low-spin). Thus, the molecules are locked either in one or the other state. Upon sublimation and deposition on a silver surface, the switches self-assemble into highly ordered arrays. Each molecule in such an array can be separately addressed with a scanning tunneling microscope and switched between the states by applying a positive or negative voltage.

Researchers from the NREL and the University of Utah have demonstrated how electron transport with a particular spin state through a two-dimensional hybrid organic-inorganic perovskite can be manipulated by introducing special organic molecules in the multilayer structure.

One way to control spin-polarized currents is through "chiral-induced" spin selectivity where the transport of electrons depends upon the transporting materials’ chirality—a structural property of a system where its mirror image is not superimposable on itself. The scientists have demonstrated how to integrate a chiral organic sublattice into an inorganic framework, creating a chiral system that can transport electrons with the desired spin control. In such systems, the chiral perovskite films act as a spin filter.

Researchers from Spain's ICN2 institute have used numerical simulations to show that spin diffusion length in graphene is independent of grain size. The researchers base their calculations on CVD grown graphene. CVD methods produces high quality materials that are built from several single-crystal sheets separated from one another through grain boundaries.

The research have shown that the grain boundaries do not have any effect on the spin transport. The researchers considered two different mechanisms for spin relaxation - randomization of spins within the grains due to spin-orbit coupling, and scattering in a grain boundary. The main implication of this research is that single-domain graphene may not be a requirement for spintronics applications.

The International Institute of Physics in Brazil recently uploaded this interesting talk by Ahmet Avsar, from the EPFL, who discusses spintronics in 2D materials (such as graphene):

This talk was given as part of the IIP's 2D Materials: From Fundamentals to Spintronics workshop which took place in early October.

An international team of researchers from France and Sweden designed a new concept of an energy harvesting engine based on spintronics and quantum thermodynamics. The basic idea is to use electron spin to harvest thermal fluctuations at room temperature.

The researchers make use of the fact that paramagnetic centers, or atom-level magnets, fluctuate their spin orientation due to heat. In the so called spin-engine, the a spontaneous bias voltage V appears between the electrodes, and thus a spontaneous current flows once the electrical circuit is closed.

There are still many challenges to create such devices (the team made some initial experiments) - but the researchers say that this concept could create chips that continuously produce electrical power with a power density that is 3x greater than raw solar irradiation on Earth.