A new way on how electron spins in layered materials can interact has been uncovered through an international collaboration between researchers from Germany, the Netherlands, and South Korea. The team published their publication in the journal Nature Materials, where the researchers report a hitherto unknown chiral coupling that is active over relatively long distances. As a result, spins in two different magnetic layers that are separated by non-magnetic materials can influence each other even though they are not adjacent.
Magnetic solids form the foundation of modern information technology. As an instance, these materials are ubiquitous in memories such as hard disk drives. The physical properties of the magnetic solids determine the functionality and efficiency of these devices. The origin of the latter is from the "concert of spins" - the interactions between microscopically small magnetic moments within the material, and understanding and directing this concert is a fundamental question for both research and applications.
Over a long distance, two magnetic materials can influence each other even if they are not on direct contact. In the past, such a long-range interaction has been observed, for instance, in heterostructures of magnetic iron layers that are separated by a thin chromium spacer. A unique fingerprint of the so-called interlayer coupling is the parallel or antiparallel alignment of the magnetic moments in the iron layers.
Technologically, this phenomenon is essential since the electrical resistance of the two possible configurations is drastically different, which is known as the giant magnetoresistance effect. It is used in operating magnetic memories and sensors, and in 2007, the Nobel Prize in Physics was awarded jointly to Peter Grunberg and Albert Fert for their discoveries.
At present, a team of scientists has now extended this "concert of spins" by a new type of long-range interlayer coupling. The group report in the journal Nature Materials that the discovered interaction leads to a unique configuration of the magnetic moments, which is neither parallel nor antiparallel but has a specific chirality. This means that the resulting arrangement of spins is not identical to its mirror image - just like a human's left hand is different from the right hand.
Such chiral interactions in crystals are quite rare in nature. Using theoretical simulations on the supercomputer JURECA in Julich, the scientists identified the interplay between the crystal structure and relativistic effects as the origin of the observed chiral interlayer coupling. This flavor of the "concert of spins" offers new opportunities for engineering complex magnetic configurations that could be useful to store and process data more efficiently in the future.