Researchers from the University of Mainz have managed to visualize the action of a third class of magnetism, called altermagnetism. Ferromagnetism and antiferromagnetism have long been known to scientists as two classes of magnetic materials. In 2019, researchers at Johann Gutenberg University Mainz (JGU) proposed a third class of magnetism called altermagnetism. Since then, this altermagnetism has been the subject of heated debate among experts, with some expressing doubts about its existence.

Recently, a group of experimental researchers led by Professor Hans-Joachim Elmers from JGU managed for the first time to measure an effect thought to be a sign of altermagnetism at DESY (Deutsches Elektronen-Synchrotron), thus providing evidence for the existence of this effect. third type magnetism. The results of the research were published at: Science Developments.

Altermannetism is a new magnetic phase

While ferromagnets, which we all know from refrigerator magnets, have all their magnetic moments pointing in the same direction, antiferromagnets have alternating magnetic moments. So, on a macroscopic level, the magnetic moments of antiferromagnets cancel each other, so there is no external magnetic field that would cause refrigerator magnets made of this material to fall off the refrigerator door. Magnetic moments in alternating magnets differ depending on how they are oriented.

“Althermagnets combine the advantages of ferromagnets and antiferromagnets. Their adjacent magnetic moments are always antiparallel to each other, as in antiferromagnets, so there is no macroscopic magnetic effect, but they also exhibit a spin-polarized current, just like ferromagnets,” explained Professor Hans-Joachim Elmers, JGU Head of the magnetism group at the Institute of Physics.

Moves in one direction with smooth rotation

Electric currents often create magnetic fields. But if we consider the alternating magnet as a whole, integrating the spin polarization in the electronic bands in all directions, it turns out that the magnetic field should be zero despite the spin polarized current. On the other hand, if attention is limited to electrons moving in a particular direction, then we can conclude that they must have a uniform spin.

“This alignment phenomenon has nothing to do with the spatial arrangement or position of the electrons, but only with the direction of the electron’s velocity,” Elmers added. Since velocity (v) times mass (M) equals momentum (P), physicists use the term “momentum space” in this context. This effect was noted by Prof in the past. Hairo Sinova and Dr. It was predicted by the JGU theoretical groups led by Libor Schmeikal.

Evidence obtained using pulsed electron microscopy

“Our team was the first to confirm the effect experimentally,” Elmers said. The researchers used a specially adapted impact microscope. For their experiments, the team exposed a thin layer of ruthenium dioxide to X-ray radiation. Excitation of the resulting electrons was sufficient for their emission and detection from the ruthenium dioxide layer. Based on the velocity distribution, the researchers were able to determine the velocity of the electrons in ruthenium dioxide. And with the help of X-rays with circular polarization, they were even able to determine the direction of rotation.

For impact microscopy, the researchers changed the focal plane normally used for observation in standard electron microscopes. Instead of an enlarged image of the surface of the ruthenium oxide film, their detectors displayed a representation of the pulse space. “Different pulses appear in different parts of the detector. Simply put, the different directions in which electrons move in the layer are represented by corresponding points in the detector,” Elmers said.

Altermannetism may also be related to spintronics. This would involve using the magnetic moments of electrons rather than their charges in dynamic random access memory. As a result, storage capacity can be increased significantly. “Our results could be a solution to a major problem in the field of spintronics,” Elmers said. “Using the potential of alternating magnets will facilitate reading stored information based on spin polarization in electronic bands.”