New fundamental physics discovered: experiments demonstrate the existence of a new type of magnetism | Top Vip News

Altermagnetism introduces a third magnetic phase, which combines the non-magnetization of antiferromagnets with the strong spin-dependent phenomena of ferromagnets. Discovered through an international collaboration, this new phase offers significant potential for spintronics, closing previous gaps in magnetic materials applications. Credit: SciTechDaily.com

Experiments at the Swiss light source SLS demonstrate the existence of a new type of magnetism, with broad implications for technology and research.

Now there is a new addition to the magnetic family: thanks to experiments at the Swiss Light Source SLS, researchers have demonstrated the existence of altermagnetism. The experimental discovery of this new branch of magnetism is reported in Nature and it means a new fundamental physics, with important implications for spintronics.

Magnetism is much more than things that stick to the refrigerator. This understanding came with the discovery of antiferromagnets almost a century ago. Since then, the family of magnetic materials has been divided into two fundamental phases: the ferromagnetic branch known for several millennia and the antiferromagnetic branch. Experimental testing of a third branch of magnetism, called altermagnetism, was carried out at the Swiss Light Source (SLS), thanks to an international collaboration led by the Czech Academy of Sciences together with the Paul Scherrer Institute (PSI).

The fundamental magnetic phases are defined by the specific spontaneous arrangements of the magnetic moments (or electron spins) and of the moment-carrying atoms in the crystals. Ferromagnets are the type of magnets that stick to the refrigerator: here the spins point in the same direction, giving a macroscopic magnetism. In antiferromagnetic materials, the spins point in alternating directions, with the result that the materials have no macroscopic net magnetization and therefore do not adhere to the refrigerator. Although other types of magnetism have been categorized, such as diamagnetism and paramagnetism, they describe specific responses to externally applied magnetic fields rather than spontaneous magnetic arrangements in materials.

Discovery and properties of altermagnets.

Altermagnets have a special combination of spin arrangements and crystalline symmetries. The spins alternate, as in antiferromagnets, which does not produce net magnetization. However, rather than simply canceling out, the symmetries give an electronic band structure with a strong spin polarization that changes direction as one passes through the material’s energy bands (hence the name altermagnets). This results in very useful properties that more closely resemble those of ferromagnets, as well as some completely new properties.

In Nature, researchers report the discovery of a new type of fundamental magnetism, called “altermagnetism.” Here, Juraj Krempasky, PSI scientist and first author of the publication, is at the Swiss light source SLS, where the experimental test of altermagnetism was carried out. Credit: Paul Scherrer Institute / Mahir Dzambegovic

Implications for spintronics

This third magnetic sibling offers distinct advantages for the developing field of next-generation magnetic memory technology, known as spintronics. While electronics uses only the charge of electrons, spintronics also takes advantage of the spin state of electrons to transport information.

Although spintronics has been promising to revolutionize information technologies for some years, it is still in its infancy. Typically, ferromagnets have been used for such devices as they offer certain strong and highly desirable spin-dependent physical phenomena. However, the macroscopic net magnetization that is useful in so many other applications poses practical limitations to the scalability of these devices, as it causes interference between bits (the information-carrying elements in data storage).

More recently, antiferromagnets have been investigated for spintronics, as they benefit from having no net magnetization and therefore offer ultrascalability and energy efficiency. However, the strong spin-dependent effects that are so useful in ferromagnets are missing, again hampering their practical applicability.

Here enter altermagnets with the best of both: zero net magnetization along with the coveted spin-dependent phenomena typically found in ferromagnets, merits that were primarily considered incompatible.

“That’s the magic of altermagnets,” says Tomáš Jungwirth, the study’s lead researcher at the Institute of Physics of the Czech Academy of Sciences. “Something that people believed was impossible until recent theoretical predictions is in fact possible.”

Theoretical predictions and experimental validation.

Not long ago, rumors began that a new type of magnetism was lurking: in 2019, Jungwirth, together with theoretical colleagues from the Czech Academy of Sciences and the University of Mainz, identified a class of magnetic materials with a spin structure that does not fit the classic descriptions. of ferromagnetism or antiferromagnetism.

In 2022, theorists published their predictions for the existence of altermagnetism. They discovered more than two hundred altermagnetic candidates in materials ranging from insulators and semiconductors, to metals and superconductors. Many of these materials have been well known and explored extensively in the past, without realizing their altermagnetic nature. Due to the enormous research and application opportunities posed by altermagnetism, these predictions caused great excitement within the community. The search was underway.

To obtain direct experimental proof of the existence of altermagnetism it was necessary to demonstrate the unique spin symmetry features predicted in altermagnets. The test was produced using angle- and spin-resolved photoemission spectroscopy on the SIS (COPHEE terminal station) and ADRESS beamlines of the SLS. This technique allowed the team to visualize a telling feature in the electronic structure of a suspected altermagnet: the splitting of electronic bands corresponding to different spin states, known as Kramers spin degeneracy lifting.

The discovery was made in manganese telluride crystals, a well-known simple two-element material. Traditionally, the material has been considered a classical antiferromagnet because the magnetic moments of neighboring manganese atoms point in opposite directions, generating a net fading magnetization.

However, antiferromagnets should not exhibit high Kramers spin degeneracy by magnetic order, while ferromagnets or altermagnets should. When scientists saw the disappearance of Kramers spin degeneracy, accompanied by the disappearance of lattice magnetization, they knew they were looking at an altermagnet.

“Thanks to the high precision and sensitivity of our measurements, we were able to detect the characteristic alternating division of energy levels corresponding to opposite spin states and thus demonstrate that manganese telluride is neither a conventional antiferromagnet nor a conventional ferromagnet, but rather It belongs to the new altermagnetic branch. of magnetic materials,” says Juraj Krempasky, beamline scientist at PSI’s Beamline Optics Group and first author of the study.

The beamlines that enabled this discovery are now dismantled, awaiting the SLS 2.0 upgrade. After twenty years of successful science, the COPHEE terminal station will be fully integrated into the new ‘QUEST’ beamline. “It was with the last photons of light from COPHEE that we performed these experiments. That they have achieved such an important scientific advance is very emotional for us,” adds Krempasky.

Conclusion and future directions

The researchers believe that this fundamental new discovery in magnetism will enrich our understanding of condensed matter physics, with impact on various areas of research and technology. In addition to its advantages for the developing field of spintronics, it also offers a promising platform for exploring unconventional superconductivity, through new insights into the superconducting states that can arise in different magnetic materials.

“Actually, altermagnetism is not something enormously complicated. It is something absolutely fundamental that was before our eyes for decades without us realizing it,” says Jungwirth. “And it’s not something that exists only in a few obscure materials. It exists in many crystals that people simply had in their drawers. In that sense, now that we have brought it to light, many people around the world will be able to work on it, which provides potential for broad impact.”

Reference: “Altermagnetic Lifting of Kramers Spin Degeneracy” February 14, 2024, Nature.
DOI: 10.1038/s41586-023-06907-7