An international team of scientists from Russia and Taiwan investigated the mechanism of the appearance of an unusual combination of magnetic properties in single crystals of Weyl semimetals — innovative materials that can be used in microelectronics and in the creation of quantum computers. In addition, the appearance of the metamagnetism effect in the Weyl semimetal was demonstrated for the first time. The results of the study are published in the scientific journal Condensed Matter.

Weyl semimetals are innovative crystal structures with an unusual state of electrons. They were described in the twentieth century, but still remain little studied experimentally. Scientists consider such structures promising for use in microelectronics and the creation of quantum computers conducting ultrafast calculations.

The uniqueness of semi-metals is that they have a non-trivial topology of electronic zones, which differs from the topology of the space around us. Topology is a characteristic of objects in terms of their transformation under the action of continuous deformation, in particular the connectivity of individual elements. For example, a ball and a bagel belong to different topological classes, since any two points of the ball can be connected to each other by a segment without going beyond it, but a bagel does not.

The addition of impurities — doping — of Weyl semimetals with paramagnetic ions can lead to the appearance of magnetic ordering in these materials, which depends on the type and concentration of impurities and seriously changes the properties of semimetals. For example, sometimes different types of magnetic order coexist in one crystal. When an internal magnetic field arises, phenomena can be observed in crystals that are generally not characteristic of pure Weyl semimetals, for example, the anomalous quantum Hall effect. However, the question of the mechanisms and causes of the appearance of such unusual properties that affect the effectiveness of the use of such materials in practice has not been sufficiently studied. Scientists of St. Petersburg University managed to understand the nature of the appearance of these properties on the example of the case of doping with iron ions.

"We carried out detailed magnetic measurements and revealed the evolution of magnetic ordering with a change in the concentration of impurities. Although ferromagnetism is the dominant type of magnetic order, in this case, reverse, antiferromagnetic properties and spatially modulated structures are also manifested. This is primarily due to the heterogeneous distribution of iron ions over the crystal volume and the complex nature of the magnetic coupling of ions," explained Elena Charnaya, Professor of the Department of Solid State Physics at St. Petersburg State University.

In addition, St. Petersburg State University physicists have discovered an interesting phenomenon in Weyl semimetals — metamagnetism caused by mobile charge carriers. This so-called band metamagnetism is characterized by a sharp increase in magnetization when an external magnetic field is applied in materials with metallic conductivity. Such effects are observed infrequently, in contrast to the well-known reorientation of spins by a magnetic field in antiferromagnets. In Weyl semimetals, the possibility of the appearance of metamagnetism was demonstrated for the first time.

The results obtained allow us to better understand the properties and mechanisms of obtaining promising materials, which is important not only from a fundamental, but also from an applied point of view — in particular, for the development of new spintronics devices that allow controlling transport using a magnetic field.

The research was carried out at the Center for Diagnostics of Functional Materials for Medicine, Pharmacology and Nanoelectronics of the St. Petersburg State University Science Park using unique equipment for accurate measurement of the magnetic properties of materials in a wide range of temperatures and magnetic fields.

Information provided by the press service of St. Petersburg State University

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