The third branch of magnetism has been demonstrated experimentally in manganese telluride, opening up opportunities for new areas of research. A recently published study Nature , shows an international group of scientists challenging the traditional division of magnetism into two types: ferromagnetism, known for thousands of years, and antiferromagnetism, identified about a century ago. Researchers have now successfully demonstrated in direct experiments the third type of magnetism (altermagnetism), which was theoretically predicted several years ago by scientists from the Johannes Gutenberg University in Mainz and the Czech Academy of Sciences in Prague.

Limitations of previously known magnetic fields for information technology

We usually think of a magnet as a ferromagnet with a strong magnetic field that holds a grocery list on the door of a refrigerator or powers the electric motor of an electric car. The magnetic field of a ferromagnet is created when the magnetic field of its millions of atoms is directed in one direction. This magnetic field can also be used to modulate electrical current in information technology (IT) components.

At the same time, the ferromagnetic field poses a serious limitation in terms of spatial and temporal scalability of components. Therefore, in recent years, great attention has been paid to the study of the second antiferromagnetic branch of magnets. Antiferromagnets are lesser-known but much more common materials in nature; The directions of atomic magnetic fields on neighboring atoms are staggered, like the colors white and black on a chessboard. Therefore, antiferromagnets generally do not create unwanted magnetic fields, but unfortunately they are so antimagnetic that they have not yet found active use in information technology.

Alternative magnets combine “incompatible” advantages

Recently designed alternative magnets combine the advantages of ferromagnets and antiferromagnets, which were considered fundamentally incompatible, and also have other unique advantages not found in other fields. Alternating magnets can be thought of as magnetic circuits in which not only the atomic moments in neighboring atoms change but also the orientation of the atoms in the crystal. So altermagnets do not create a magnetic field outside, but the electrons inside actually experience a magnetic field 1000 times stronger than the field of the refrigerator magnet. These domains can modulate electrical currents similarly to ferromagnets and are therefore potentially very attractive for future ultrascale nanoelectronics applications.

In addition, scientists have identified more than 200 candidate materials for altermagnetism, with properties that include insulators, semiconductors, metals, and even superconductors. Research groups have studied many of these materials in the past, but their alternative magnetic nature has been hidden from them.

Theorists predicted an alternative magnetic branch five years ago

Starting in 2019, a team from the Johannes Gutenberg University in Mainz and the Institute of Physics in Prague published a series of papers in which they theoretically described unconventional magnetic materials. In 2021, Dr. The same team, consisting of Libor Schmeikal, Professor Hyro Sinov and Professor Thomas Jungwirth, predicted that these materials generate a third fundamental type of magnetism, which they call altermagnetism, whose crystalline and magnetic structure is completely different from ordinary ferromagnets and antiferromagnets. . .

The theoretical prediction was immediately followed by a wave of further research by research groups from around the world, as alternativemagnetism opened vast and unprecedented opportunities for research and application. The question then arose of when direct experimental evidence would be available.

Experimental data conducted on a material considered for decades to be a “classical antiferromagnet”

An international team of researchers presented such evidence in a study published in 2017. Nature. The researchers decided to examine crystals of manganese telluride (MnTe), a simple two-element alternative magnetic candidate. Traditionally, this material is considered one of the classical antiferromagnets, because the magnetic moments in neighboring manganese atoms are directed in opposite directions and therefore do not create an external magnetic field around the material.

Now scientists have managed to directly demonstrate the altermagnetism of MnTe for the first time. They used theoretical predictions to determine in which direction light would “shine” on high-quality MnTe crystals in a photoemission experiment. The team measured band structures, which are maps that physicists use to describe the properties of electrons in crystals, at the synchrotron. They were then able to show that there is strong spin-splitting of electronic states in MnTe, despite the absence of an external magnetic field. The scale and shape of the spin split perfectly matches the alternative magnetic split predicted using quantum mechanical calculations.

The researchers were also able to detect the spin polarization of the bands for the first time. The lead author of the theoretical part of the paper is Dr. “This is direct evidence that MnTe is neither a conventional antiferromagnet nor a conventional ferromagnet, but belongs to a new alternativemagnetic branch of magnetic materials,” said Libor Schmeikal.

The study was conducted in collaboration with scientists from the Czech Academy of Sciences in Prague, the Paul Scherrer Institute in Switzerland, the University of West Bohemia in Pilsen, drawing on the expertise of researchers from the Mainz Institute of Physics at Johannes Gutenberg University in Germany. University of Linz in Austria, University of Nottingham in England and Charles University in Prague

Discovery of alternative magnetism opens new research directions

from the University of Mainz. “Following the initial predictions and considering the rapidly growing interest in altermagnetism worldwide, we are pleased to be able to contribute to the experimental demonstration of MnTe,” said Libor Schmeikal.

Professor Hairo Sinova, director of the Interdisciplinary Spintronics Research Group (INSPIRE) and Interdisciplinary Spin Phenomena Center (SPICE) at JGU and co-author of the study, added: “The discovery of altermagnetism has opened new directions for global research on highly scalable and energy-efficient IT components.” transforms it into new physical and material principles for The field in particular is heating up, and other studies have recently emerged confirming other properties of alternative magnetic materials. So the discovery of altermagnetism appears to be just the beginning of an exciting new era in magnetism.