Three distinct variants of magnetic domain walls discovered in helimagnetic iron germanium (FeGe)

Researchers have discovered three distinct variants of magnetic domain walls in iron-germanium (FeGe) hemagnet. Their results were published in Natural Physics. Researcher Dennis Meier, an associate professor at the Norwegian University of Science and Technology (NTNU), says understanding the creation of magnetic fields is key to understanding the significance of the discovery.

An electric current can generate a magnetic field, as in electromagnets. The second source of an electric field is spin, which is the magnetic moment of the elementary particles of an atom. The best known type of magnetism is ferromagnetism. This type of magnetic order occurs when the magnetic moments of the atoms of a substance are essentially aligned, that is, they point in the same direction and attract or repel other magnetic objects.

With helimagnets, the magnetic moments of atoms are organized in spirals or helices. Iron germanium (FeGe) is a mixture of iron and metalloid germanium. It has a crystal structure similar to that found in a diamond, in which the same pattern of atoms repeats. In reality, this material is not as uniform as it seems. The crystal may be near perfect, but the magnetic structure may simultaneously have its own organization.

In other words, a seemingly perfect crystal structure in a solid is divided into separate zones, each with its own particular magnetic properties. These magnetic regions are called domains. In ferromagnets, atoms in each of these domains have magnetic moments pointing in the same direction, but the direction varies between neighboring areas. Helimagnets instead have domains with spiral patterns. The transitions between these areas are called domain walls, which is what Meier and his colleagues study.

The international research group discovered three new classes of domain walls in helimagnets. “The special patterns occur because of so-called topological defects. The researchers were lucky to find them,” says Meier. “But you have to know when you’re lucky.”

Their findings are completely new to science. Domain walls can have exotic magnetic properties that the regions they separate do not reveal. Walls, for example, can interact more strongly with an electric current and could potentially be used for data transfer and storage in the future. This discovery could one day provide an alternative to today’s computers, which invert the magnetic field and switch the voltage between one and zero. This method is much more energy intensive than moving topological magnetic structures along what is called running memory.

“The next thing we’re going to do is try to influence these new domain walls,” Meier says. The researchers will try to direct these walls with an electric current, that is to say to control them. For this project, Meier and his team from the Department of Materials Science and Engineering will collaborate with colleagues from the new QuSpin (Center for Quantum Spintronics) Center of Excellence at NTNU.