Physicists create the first two-dimensional ferrimagnetism in graphene

Scientists from the University of Saint Petersburg together with their foreign colleagues have created the world’s first two-dimensional ferromagnetism in graphene. The use of the magnetic state obtained from graphene can become the basis of a new approach to electronics, increasing its energy efficiency and speed when developing devices that use alternative technologies without the use of silicon.

Graphene, a two-dimensional modification of carbon, is the lightest and strongest of all the two-dimensional materials available today, and it is also highly conductive. In 2018, researchers from the University of Saint Petersburg, together with their colleagues from Tomsk State University and German and Spanish scientists, were the first in the world to modify graphene and give it the properties of cobalt and gold: magnetism and spin-orbit interaction (between the moving electron in graphene and its own magnetic moment). By interacting with cobalt and gold, graphene not only retains its unique characteristics, but also partially acquires the properties of these metals.

As part of the new work, the scientists synthesized a system with a ferrimagnetic state of graphene. It is a unique state in which the substance has magnetization in the absence of an external magnetic field. The physicists used a similar substrate made of a thin layer of cobalt and a gold alloy on its surface.

During surface alloying, dislocation loops formed under the graphene. These loops are triangular regions with a lower density of cobalt atoms than that of gold atoms. Until now, it was known that single-layer graphene could only be fully magnetized in a uniform way. However, studies by scientists at St. Petersburg University have shown that it is possible to control the magnetization of individual sublattice atoms through selective interaction with structural defects in the substrate.

“This is a significant discovery, as all electronics devices they use electrical charges and involve the generation of heat when current flows. Our research will eventually allow information to be transmitted in the form of spin currents. This is a new generation of electronics, a fundamentally different logic and a new approach to technological development that reduces power consumption and increases the speed of information transfer,” explained Artem Rybkin, principal investigator of the research, a principal research associate at the Laboratory of Spin and Electronic Structure of Nanosystems at Saint Petersburg University.

The second important feature of the graphene synthesized by the physicists at the University of Saint Petersburg is the strong spin-orbit interaction. In this structure, the strengthening of this interaction is explained by the presence of gold atoms under the graphene. In a certain proportion of the magnetic and spin-orbit interaction parameters, it is possible to pass from the trivial, ie familiar, state of graphene to a novel, topological.

The research results are published in Physical Review Letters.