Antiferromagnetism

Researchers from Johannes Gutenberg-University Mainz, ALBA Synchrotron Light Facility and Tohoku University have identified quasiparticles called merons in a synthetic antiferromagnet for the first time, which could lead to new concepts for spintronics devices.

The spintronics field is still rather nascent as research is ongoing. Recent research has focused on structures called skyrmions as potential building blocks. These structures are quasiparticles made up of numerous electron spins and can be thought of as two-dimensional whirls (or “spin textures”) within a material. Skyrmions exist in many magnetic materials, including cobalt–iron–silicon and the manganese–silicide thin films in which they were first discovered. They are attractive spintronics candidates because they are robust to external perturbations, making them particularly stable for storing and processing the information they contain. At just tens of nanometres across, they are also much smaller than the magnetic domains used to encode data in today’s disk drives, making them ideal for future data storage technologies such as “racetrack” memories. Like skyrmions, merons are made up of numerous individual spins. Unlike them, their stray magnetic fields are miniscule, which would facilitate ultrafast operations and even higher information storage densities within a device. Until now, however, merons have only been observed in natural antiferromagnets, where they have proved difficult to analyze and manipulate.

Zhengzhou University researchers have synthesized a new material that combines graphene's remarkable properties with a strong response to magnetic fields. 

Graphene has a long spin lifetime and hyperfine interactions, making it potentially favorable for spintronics applications. Despite the recent discoveries of spin-containing graphene materials, graphene-based materials with room-temperature macroscopic ferromagnetism are extremely rare. In their recent study, room-temperature ferromagnetic amorphous graphene oxide (GO) was synthesized by introducing abundant oxygen-containing functional groups and C defects into single-layered graphene, followed by a self-assembly process under supercritical CO₂ (SC CO₂). 

One way of processing information in spintronics is to use the magnetic vortices called skyrmions or, alternatively, their still little understood and rarer cousins called 'merons'. Both are collective topological structures formed of numerous individual spins. Merons have to date only been observed in natural antiferromagnets, where they are difficult to both analyze and manipulate.

Working in collaboration with teams at Tohoku University in Japan and the ALBA Synchrotron Light Facility in Spain, researchers of Johannes Gutenberg University Mainz (JGU) have been the first to demonstrate the presence of merons in synthetic antiferromagnets and thus in materials that can be produced using standard deposition techniques.

Researchers at the Czech Academy of Sciences, Institut Polytechnique de Paris, Vienna Technical University (TU Wien), Charles University, Malvern Panalytical B.V., Nuclear Physics Institute CAS and the European Commission's Joint Research Centre (JRC) recently made an important step that could advance the field of spintronics: they managed to switch the spins in an antiferromagnetic material using surface strain. 

"There are different types of magnetism," explains Sergii Khmelevskyi from the Vienna Scientific Cluster Research Center, Vienna Technical University. "The best known is ferromagnetism. It occurs when the atomic spins in a material are all aligned in parallel. But there is also the opposite, antiferromagnetism. In an antiferromagnetic material, neighboring atoms always have opposite spins." Their effects therefore cancel each other out and no magnetic force can be detected from the outside.

Researchers have conducted experiments at the Swiss Light Source SLS that resulted in proof of the existence of a new type of magnetism: altermagnetism. The experimental discovery of this new branch of magnetism could signify new fundamental physics, with major implications for spintronics.

Since the discovery of antiferromagnets nearly a century ago, the family of magnetic materials has been divided into two fundamental phases: the ferromagnetic branch known for several millennia and the antiferromagnetic branch. The experimental proof of a third branch of magnetism, termed altermagnetism, was made by an international collaboration led by the Czech Academy of Sciences together with Paul Scherrer Institute PSI. The fundamental magnetic phases are defined by the specific spontaneous arrangements of magnetic moments—or electron spins—and of atoms that carry the moments in crystals.

An interdisciplinary collaboration of researchers from South Korea and Singapore recently reported a significant advance towards achieving spin-polarized van der Waals heterostructures. The team designed a spin-selective memtransistor device using single-layer graphene deposited on the antiferromagnetic van der Waals magnetic insulator CrI₃. 

Transport measurements combined with first-principles calculations provide unprecedented insights into tailoring reciprocal magnetic proximity interactions to generate and probe proximitized magnetism in graphene at room temperature.

Researchers have devised a new ultrafast method for controlling magnetic materials, that may enable next-generation information processing technologies.

A possible solution for building faster systems for processing is to use patterns of electron spins, called spin waves, to transfer and process information much more rapidly than in conventional computers. So far, a major challenge has been in manipulating these ultrafast spin waves to do useful work. Announcing a significant step forward, researchers from The University of Texas at Austin and MIT have developed a method to precisely manipulate these ultrafast spin waves using tailored light pulses. Their findings are detailed in two studies in Nature Physics, led by MIT graduate student Zhuquan Zhang, University of Texas at Austin postdoctoral researcher Frank Gao, MIT’s professor of chemistry Keith Nelson and UT Austin assistant professor of physics Edoardo Baldini.

Researchers from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), led by Associate Prof. Li Xingxing and Prof. Yang Jinlong, recently developed a novel chemical method for two-dimensional metal-organic lattices.

In spintronics, it is paramount to develop an efficient way to reversibly control the spin order of materials. Though various physical methods have been proposed, chemically achieving this has posed significant challenges. The researchers proposed the utilization of the well-recognized lactim−lactam tautomerization process to reversibly modulate the magnetic phase transition in two-dimensional (2D) organometallic lattices. This could offer new pathways for controlling the electrical and magnetic characteristics of materials.

Researchers at China's Hefei University of Technology, University of Science and Technology of China, South China University of Technology, Chinese Academy of Sciences (CAS), Anhui University, Australia's RMIT University, University of New South Wales, Saudi Arabia's Al-Baha University and University of Jeddah have reported magnetism in a quasi-2D magnet Cr_1.2Te₂, observed at room temperature (290 K). 

By intercalating protons into van der Waals ferromagnet Cr_1.2Te₂ nanoflakes, the group of researchers successfully induced a room-temperature magnetic phase transition from ferromagnetism to antiferromagnetism.

Researchers at Johannes Gutenberg University Mainz, the University of Konstanz and Tohoku University in Japan have increased the diffusion of magnetic whirls, so called skyrmions, by a factor of ten.

Science often does not simply consider the spin of an individual electron, but rather magnetic whirls composed of numerous spins. These whirls, called skyrmions, emerge in magnetic metallic thin layers and can be considered as two-dimensional quasi-particles. On the one hand, the whirls can be deliberately moved by applying a small electric current to the thin layers; on the other hand, they move randomly and extremely efficiently due to diffusion. The feasibility of creating a functional computer based on skyrmions was demonstrated by a team of researchers from Johannes Gutenberg University Mainz (JGU), led by Professor Dr. Mathias Kläui, using an initial prototype. This prototype consisted of thin, stacked metallic layers, some only a few atomic layers thick.