Researchers create chiral antiferromagnetic network

2 December 2025, by MIN-Dekanat

Photo: UHH/Kubetzka

Scanning tunneling microscopy measurement of the antiferromagnetic domain wall network. Domain walls appear bright, while the very bright white areas indicate argon bubbles with domain wall branches containing up to six domain walls. The width of the image is approximately 120 nanometers.

Researchers from the Department of Physics at the University of Hamburg have created a magnetic network on the nanometer scale in an antiferromagnetic manganese layer. The transitions between different magnetically ordered areas (domains) of the network were imaged on the atomic scale using scanning tunneling microscopy, and the intersection points of the domain walls exhibited chirality. The observed chirality can be explained by a magnetically driven shearing of the manganese layer, as theoretical physicists at Kiel University (CAU) were able to demonstrate. The results of this collaboration were published in the journal 'Nature Communications'.

The magnet we use to attach our notes to the refrigerator is made of a ferromagnetic material. On a microscopic scale, all the “atomic bar magnets” in such a ferromagnet are aligned parallel to each other. Ferromagnetic materials are used in many applications today, from compasses and magnetic sensors to magnetic data storage devices. Almost 100 years ago, French researcher Louis Néel discovered that there are also many materials in nature in which the “atomic bar magnets” are aligned oppositely to each other in neighboring positions in the crystal lattice. He called these materials antiferromagnets and was awarded the Nobel Prize in Physics in 1970 for this discovery, among other things. Due to the antiparallel alignment of the bar magnets on the atomic scale, antiferromagnets do not generate a magnetic field around them and are therefore not suitable for attaching notes to the refrigerator, for example. Since antiferromagnetic order is also difficult to detect, these materials were long considered unsuitable for technical applications.

However, it has since become apparent that antiferromagnetic materials are promising candidates for applications in magnetoelectronics. In this field, electric currents are used to manipulate and read out the magnetic properties of materials. Due to this potential, antiferromagnets have become the focus of current research. At the same time, complex magnetic networks are interesting candidates for novel, unconventional computers because they exhibit several different unique transport properties, including strong interactions of currents with three-dimensional magnetic structures in which the atomic bar magnets can point in all spatial directions.

The team of researchers from the Universities of Hamburg and Kiel investigated a model system for an antiferromagnet at an interface: a layer of manganese atoms only two atomic layers thick, grown on the surface of an iridium crystal. The Hamburg researchers used spin-polarized scanning tunneling microscopy to image the magnetic order in this manganese film – a microscopy technique that allows magnetic structures to be resolved down to the atomic scale.

“In the scanning tunneling microscopy images, a complex magnetic network of domain walls appeared between antiferromagnetically ordered areas. We could see that it was generated by the implanted argon bubbles,” explains project leader Dr. Kirsten von Bergmann from the Department of Physics at the University of Hamburg:  “At the intersections of three domain walls, we found, on the one hand, a structural handedness and, on the other hand, that the ‘atomic bar magnets’ point in the directions of the corners of a tetrahedron, meaning they have an angle of approximately 109.47° to each other” (see Fig. 1).

Using quantum mechanical ab-initio calculations performed on supercomputers belonging to the National High Performance Computing Association (NHR), researchers at Kiel University were able to show that magnetic exchange forces cause a lateral shift in the top layer of the manganese layers. “This leads to considerable strain at points where different alignments of the magnetic state meet and may explain the observed handedness at the intersection points,” explains Professor Stefan Heinze from Kiel University. In addition, the Kiel researchers were able to explain how the three-dimensional magnetic structure at the intersection points is formed and how the magnetic coupling between the two layers occurs (Fig. 2).

.

The formation of domain wall junctions at implanted argon bubbles can be regarded as a reciprocal effect, in which the induced local stress selects a specific orientation of the magnetically induced shear of the magnetic film. The ab-initio calculations show that, at the same time, the non-coplanar magnetic order at the emerging domain wall junctions has topological properties. This work provides a proof-of-principle demonstrating how the close relationship between structure and magnetism can be exploited to create complex antiferromagnetic networks.