Memory

Scientists have been looking for efficient methods to generate spin current. The photogalvanic effect, a phenomenon characterized by the generation of DC current from light illumination, is particularly useful in this regard. Studies have found that a photogalvanic spin current can be generated similarly using the magnetic fields in electromagnetic waves. However, there's a need for candidate materials and a general mathematical formulation for exploring this phenomenon.

Now, Associate Professor Hiroaki Ishizuka from Tokyo Institute of Technology (Tokyo Tech), along with his colleague Masahiro Sato, addressed these issues. In their recent study, they presented a general formula that can be used to calculate the photogalvanic spin current induced by transverse oscillating magnetic excitations. They then used this formula to understand how photogalvanic spin currents arise in bilayer chromium (Cr) trihalide compounds, namely chromium triiodide (CrI₃) and chromium tribromide (CrBr₃).

Researchers from the University of Tokyo and CREST (Japan Science and Technology Agency) have explored the world of spintronics and other related areas of solid state physics with a focus on antiferromagnets. The team has reported, in its recent study, the experimental realization of perpendicular and full spin–orbit torque switching of an antiferromagnetic binary state.

The team used the chiral antiferromagnet Mn₃Sn, which exhibits the magnetization-free anomalous Hall effect owing to a ferroic order of a cluster magnetic octupole hosted in its chiral antiferromagnetic state. They fabricated heavy-metal/Mn₃Sn heterostructures by molecular beam epitaxy and introduce perpendicular magnetic anisotropy of the octupole using an epitaxial in-plane tensile strain. By using the anomalous Hall effect as the readout, the team demonstrated 100% switching of the perpendicular octupole polarization in a 30-nanometre-thick Mn₃Sn film with a small critical current density of less than 15 megaamperes per square centimeter. Their theory is that the perpendicular geometry between the polarization directions of current-induced spin accumulation and of the octupole persistently maximizes the spin–orbit torque efficiency during the deterministic bidirectional switching process. The team's recent work provides a significant basis for antiferromagnetic spintronics.

A joint research group that included scientists from Osaka University, Tokyo Institute of Technology and University of York has achieved what is reportedly the world's highest level performance index (magnetic electrical coupling coefficient) in developing a high-performance interfacial multiferroic structure for new voltage information writing technology in spintronics devices. At the same time, they successfully demonstrated repeated switching of nonvolatile memory states by applying an electric field.

A challenge for magnetoresistive memory (MRAM), which is expected to become the next-generation of nonvolatile memory devices, is that it consumes a large amount of power because current is passed through its metallic magnetic material when information is written. The research group has demonstrated a high-performance interfacial multiferroic structure consisting of a high-performance metallic magnetic material and a piezoelectric material bonded together using their own technology, and developed a technology to switch the magnetization direction of the metallic magnetic material efficiently by simply applying voltage instead of an electric current.

A new study, coordinated by ICN2 group leaders and ICREA professors Prof. Stephan Roche and Prof. Sergio O. Valenzuela, and by Prof. Hyunsoo Yang from the National University of Singapore, examined the current developments and challenges in regards to MRAM, and outlined the opportunities that can arise by incorporating two-dimensional material technologies. It highlighted the fundamental properties of atomically smooth interfaces, the reduced material intermixing, the crystal symmetries and the proximity effects as the key drivers for possible disruptive improvements for MRAM at advanced technology nodes.

The research was carried out by a collaboration of various members of the Graphene Flagship project consortium, including various institutes of the Centre national de la recherche scientifique (CNRS, France), Imec (Belgium), Thales Research and Technology (France), and the French Atomic Energy Commission (CEA), as well as key industries such as Samsung Electronics (South Korea) and Global Foundries (Singapore).

Researchers at Cornell University and University of Nebraska have discovered a strategy to switch the magnetization in thin layers of a ferromagnet. This a technique has the potential to lead to the development of more energy-efficient magnetic memory devices.

Scientists have been trying for many years to change the orientation of electron spins in magnetic materials by manipulating them with magnetic fields. But researchers including Dan Ralph, the F.R. Newman Professor of Physics in the College of Arts and Sciences and the paper's senior author, have instead looked to using spin currents carried by electrons, which exist when electrons have spins generally oriented in one direction.

University of Nebraska-Lincoln's scientist Christian Binek and University at Buffalo's Jonathan Bird and Keke He have teamed up to develop the first magneto-electric transistor.

Along with curbing the energy consumption of any microelectronics that incorporate it, the team's design could reduce the number of transistors needed to store certain data by as much as 75%, said Nebraska physicist Peter Dowben, leading to smaller devices. It could also lend those microelectronics steel-trap memory that remembers exactly where its users leave off, even after being shut down or abruptly losing power.

Scientists from MIT, Arizona State University, National Institute for Materials Science in Tsukuba, Université de Liège in Belgium and Italy's CNR-SPIN have discovered an exotic "multiferroic" state in a material that is as thin as a single layer of atoms.

Their observation is the first to confirm that multiferroic properties can exist in a perfectly two-dimensional material. The findings could pave the way for developing smaller, faster, and more efficient data-storage devices built with ultrathin multiferroic bits, as well as other new nanoscale structures.

A research team from Brown University has found a surprising new phenomenon that can arise in 'magic-angle graphene' - two sheets of graphene that are stacked together at a particular angle with respect to each other, giving rise to various fascinating behaviors. In a recent research, the team showed that by inducing a phenomenon known as spin-orbit coupling, magic-angle graphene becomes a powerful ferromagnet.

"Magnetism and superconductivity are usually at opposite ends of the spectrum in condensed matter physics, and it's rare for them to appear in the same material platform," said Jia Li, an assistant professor of physics at Brown and senior author of the research. "Yet we've shown that we can create magnetism in a system that originally hosts superconductivity. This gives us a new way to study the interplay between superconductivity and magnetism, and provides exciting new possibilities for quantum science research."

Researchers at Tohoku University and the University of Gothenburg have designed a new spintronics technology for brain-inspired computing.

Sophisticated cognitive tasks, such as image and speech recognition, have seen recent breakthroughs thanks to deep learning. Even so, the human brain still executes these tasks without exerting much energy and with greater efficiency than any computer. The development of energy-efficient artificial neurons capable of emulating brain-inspired processes has therefore been a major research goal for decades.

Researchers from Berkeley Lab, UC Berkeley, UC Riverside, Argonne National Laboratory, Nanjing University and the University of Electronic Science and Technology of China, have developed an ultrathin magnet that operates at room temperature. This development could lead to new applications in computing and electronics - such as high-density, compact spintronic memory devices - and new tools for the study of quantum physics.

"We're the first to make a room-temperature 2D magnet that is chemically stable under ambient conditions," said senior author Jie Yao, a faculty scientist in Berkeley Lab's Materials Sciences Division and associate professor of materials science and engineering at UC Berkeley. "This discovery is exciting because it not only makes 2D magnetism possible at room temperature, but it also uncovers a new mechanism to realize 2D magnetic materials," added Rui Chen, a UC Berkeley graduate student in the Yao Research Group and lead author on the study.