Antiferromagnetism

Researchers from Kyoto University, Chiba University, The University of Tokyo, Osaka University and Tokai University have found that the direction of spins inside a special type of magnet can be changed rapidly - flipping about every trillionth of a second - without increasing the temperature. They achieved this by applying a strong magnetic field with an oscillation frequency in the terahertz range.

The background for this work, according to the scientists, is the ever-increasing amount of information handled by computers and communication devices, that is driving development of technologies using the terahertz band - around 1012 Hz, a frequency range beyond the conventional gigahertz range of 109 Hz - considered important for the post-5G era. Additionally, memory technologies based on spintronics are expected to use less power to store more information, with antiferromagnets attracting attention because their collective spin-motion mode frequency reaches the terahertz range, making it possible to control spins using terahertz waves. However, conventional spin excitation using electric-field pulses is accompanied by heating or carrier excitation effects that subside relatively slowly, making it difficult to achieve fast spin control. The team has now demonstrated non-thermal spin switching in a canted antiferromagnet by dynamically modifying the magnetic energy landscape using a strong multicycle terahertz magnetic near-field.

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.

Researchers at Osaka Metropolitan University, University of Nottingham, Czech Academy of Sciences, Diamond Light Source, ohannes Kepler University Linz, Johannes Gutenberg Universität Mainz, TU Wien and Masaryk University have used symmetry, ab initio theory, and experiments to explore x-ray magnetic circular dichroism (XMCD) in the altermagnetic class. The international research group recently pioneered a new method to identify altermagnets, using manganese telluride (α-MnTe) as a testbed. 

Magnetic materials have traditionally been classified as either ferromagnetic or antiferromagnetic. However, there appears to be a third class of magnetic materials exhibiting what is known as 'altermagnetism'. In ferromagnetic materials, all the electron spins point in the same direction, while in antiferromagnetic materials, the electron spins are aligned in opposite directions, half pointing one way and half the other, canceling out the net magnetism. Altermagnetic materials are proposed in theory to possess properties combining those of both antiferromagnetic and ferromagnetic materials. One potential application of altermagnetic materials is in spintronics technology, which aims to utilize the spin of electrons effectively in electronic devices such as next-generation magnetic memories. However, identifying altermagnets has been a challenge.

An international team of researchers, led by scientists from the CNRS, has reported that the magnetic nanobubbles known as skyrmions can be moved by electrical currents, attaining record speeds up to 900 m/s.

Magnetic skyrmions are topological magnetic textures that hold great promise as nanoscale bits of information in memory and logic devices. While room-temperature ferromagnetic skyrmions and their current-induced manipulation have been demonstrated, their velocity has thus far been limited to about 100 meters per second, which is too slow for computing applications. In addition, their dynamics are perturbed by the skyrmion Hall effect, a motion transverse to the current direction caused by the skyrmion topological charge. 

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.