Research / Technical

Researchers at Tohoku University and the University of California, Santa Barbara, have developed new computing hardware that utilizes a Gaussian probabilistic bit made from a stochastic spintronics device. This innovation is expected to provide an energy-efficient platform for generative AI.

As Moore's Law slows down, domain-specific hardware architectures - such as probabilistic computing with naturally stochastic building blocks - are gaining prominence for addressing computationally hard problems. Similar to how quantum computers are suited for problems rooted in quantum mechanics, probabilistic computers are designed to handle inherently probabilistic algorithms. These algorithms have applications in areas like combinatorial optimization and statistical machine learning. 

A team of researchers from CIC nanoGUNE, IKERBASQUE, IMEC and CNRS have reported a spintronic device that leverages proximity effects alone, specifically a 2D graphene-based spin valve. The functioning of this valve relies only on the proximity to the van der Waals magnet Cr₂Ge₂Te₆. Spin precession measurements showed that the graphene acquires both spin–orbit coupling and magnetic exchange coupling when interfaced with the Cr₂Ge₂Te₆. This leads to spin generation by both electrical spin injection and the spin Hall effect, while retaining spin transport. The simultaneous presence of spin–orbit coupling and magnetic exchange coupling also leads to a sizeable anomalous Hall effect.

The primary objective of this recent study was to tackle a long-standing research challenge, namely that of realizing the first-ever seamless 2D spintronic device. The spin valve they developed could enable the manipulation and transport of spin entirely in the 2D plane.

Magnetic skyrmions have so far been treated as two-dimensional spin structures characterized by a topological winding number. However, in real systems with the finite thickness of the device material being larger than the magnetic exchange length, the skyrmion spin texture extends into the third dimension and cannot be assumed as homogeneous.

A 3D reconstruction of a skyrmion derived from X-ray images. Credit: Berkeley Lab

Researchers at Lawrence Berkeley National Laboratory, Swiss Light Source (Paul Scherrer Institute) and Western Digital Research Center have used soft x-ray laminography to reconstruct, with about 20-nanometer spatial (voxel) size, the full three-dimensional spin texture of a skyrmion in an 800-nanometer-diameter and 95-nanometer-thin disk patterned into a 30× [iridium/cobalt/platinum] multilayered film.

In a recent sturdy, researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory and Northern Illinois University discovered that they could use light to detect the spin state in a class of materials called perovskites (specifically in this research methylammonium lead iodide, or MAPbI₃). 

To understand spin, consider electrons orbiting the atomic nucleus. When atoms are close together, they can share some of their outer electrons, which creates a bond between them. Each bond contains two electrons that are ​“paired,” meaning they share an orbital — the region where they move. Now, each of these paired electrons has one of two possible spin states: spin up or spin down. If one electron is spin up, the other is spin down. Since we can’t know exactly which electron has which spin without looking at them, we say they exist in a quantum superposition — a state where they are both spin up and spin down until observed.

researchers at the University of Illinois Urbana-Champaign have used new a experimental technique to measure heating in spintronic devices, allowing direct comparison to other effects. The researchers say that this technique can be used to select spintronic materials whose magnetic behavior is minimally impacted by heating, leading to faster devices.

"Spintronic devices depend on the ability to change magnetization using electric currents, but there are two possible explanations for it: electromagnetic interactions with the current, or the increase in temperature caused by the current," said Axel Hoffmann, project lead and Illinois materials science and engineering professor. "If you want to optimize the function of the device, you have to understand the underlying physics. That's what our approach helped us to do."

Researchers from the University of Nebraska-Lincoln and University of Latvia have announced "a breakthrough in antiferromagnetic spintronics" that could expand the nanotechnology’s capabilities, which have been limited by their need for excessive power. 

The team showed that introducing boron — a process called B-doping — into magnetoelectric oxides can control magnetic fields at the high temperatures prevalent in electronics. This long has been the “holy grail” of such research, said Christian Binek, Charles Bessey Professor of physics.

A Spanish-German collaboration recently studied graphene-cobalt-iridium heterostructures at BESSY II. The results show how two desired quantum-physical effects reinforce each other in these heterostructures, which could lead to new spintronic devices based on these materials.

Spintronics uses the spins of electrons to perform logic operations or store information. Ideally, spintronic devices could operate faster and more energy-efficiently than conventional semiconductor devices. However, it is still difficult to create and manipulate spin textures in materials. Graphene, a 2D honeycomb structure made of carbon atoms, is considered an interesting candidate for spintronic applications. Graphene is typically deposited on a thin film of heavy metal. At the interface between graphene and heavy metal, a strong spin-orbit coupling develops, which gives rise to different quantum effects, including a spin-orbit splitting of energy levels (Rashba effect) and a canting in the alignment of spins (Dzyaloshinskii-Moriya interaction). The spin canting effect is especially needed to stabilize vortex-like spin textures, known as skyrmions, which are particularly suitable for spintronics.

Researchers from Delft University of Technology and Karlsruhe Institute of Technology (KIT) have initiated a controlled movement in the heart of an atom, causing the atomic nucleus to interact with one of the electrons in the outermost shells of the atom. This electron could be manipulated and read out through the needle of a scanning tunneling microscope. The research offers prospects for storing quantum information inside the nucleus, where it is safe from external disturbances.

The team studied a single titanium atom - a Ti-47 atom, that has one neutron less than the naturally abundant Ti-48, which makes the nucleus slightly magnetic. This magnetism, or the 'spin', can be seen as a sort of compass needle that can point in various directions. The orientation of the spin at a given time constitutes a piece of quantum information.

Researchers from Monash University, part of the FLEET Centre, and China's Weifang University, have reported a generic approach towards intrinsic magnetic second-order topological insulators - materials that can be beneficial for spintronics.

Two-dimensional ferromagnetic semiconductors, such as CrI₃, Cr₂Ge₂Te₆, and VI₃, have been extensively studied in recent years and are fundamental to spintronics. Topological insulators are materials with unique properties where the interior is insulating, but the boundary can conduct electrons. In three-dimensional topological insulators like Bi₂Se₃, the surface hosts two-dimensional Dirac fermions. Second-order topological insulators, a new concept extending the idea of topological insulators, exhibit (m-2)-dimensional boundary states in m-dimensional materials, such as one-dimensional hinge states in three-dimensional materials and zero-dimensional corner states in two-dimensional materials.

Researchers at King Abdullah University of Science and Technology (KAUST) and Khalifa University of Science and Technology have investigated the transmission, tunneling magnetoresistance ratio and spin injection efficiency of bilayer LaI₂ using a combination of first-principles calculations and the non-equilibrium Green’s function method. 

Multilayer graphene electrodes were used by the team, to build a magnetic tunnel junction with bilayer LaI₂ as ferromagnetic barrier. The magnetic tunnel junction reportedly proved to be a perfect spin filter device with an impressive tunneling magnetoresistance ratio of 653% under a bias of 0.1 V and a still excellent performance in a wide bias range. The team said that in combination with the obtained high spin injection efficiency, this could hold great potential from an application point of view.