Memory

Researchers at Switzerland EPFL, China's Anhui University, Germany's University of Cologne and University of New Hampshire in the US have developed a technique that can visualize and control the rotation of a handful of spins arranged in a vortex-like texture at the fastest speed ever achieved. The breakthrough can advance spintronics devices like computer memory, logic gates, and high-precision sensors.

"The visualization and deterministic control of very few spins has not yet been achieved at the ultrafast timescales," says Dr. Phoebe Tengdin, a postdoc at EPFL, pointing out the very tight timeframes that this control needs to happen for spintronics to ever make the leap into applications. Now, the team developed a new technique that can visualize and control the rotation of a handful of spins arranged in a vortex-like texture, a kind of spin "nano-whirlpool" called a skyrmion.

A team led by researchers at the National Institute of Standards and Technology (NIST), the University of South Florida (USF), Harvey-Mudd College and the University of the District of Columbia has discovered a route toward reducing the sputter damage during growth of Nanolayered Pt/Co/Ir-based Synthetic Antiferromagnets that delivers significant improvements in perpendicular magnetic anisotropy and interlayer exchange coupling energy.

Synthetic antiferromagnets (SAFs) are a core component for top-pinned magnetic tunnel junction memory systems in semiconductor production. Establishing low-damage sputtering techniques to protect the multiple interfaces between sub-nm thick constituent layers delivers improved SAF properties could be key to data retention in high-density, sub-10 nm diameter magnetic memory arrays.

Researchers from Germany's Max Planck Institute of Microstructure Physics have reported a lift-off and transfer method to fabricate three-dimensional racetrack memories from freestanding magnetic heterostructures grown on a water-soluble sacrificial release layer.

The fabrication of three-dimensional nanostructures is key to the development of next-generation nanoelectronic devices with a low device footprint. Magnetic racetrack memories encode data in a series of magnetic domain walls that are moved by current pulses along magnetic nanowires. To date, most studies have focused on two-dimensional racetracks.

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.