Let there be magnetism

ACS Nano http://doi.org/fx2ct5 (2012)

Two-dimensional materials such as graphene and molybdenum sulphide have mechanical and electronic properties that are useful for a variety of applications, but they are non-magnetic. These materials can be made magnetic by, for example, introducing transition metal atoms or point defects, but the resulting materials lack the stability and controllability needed for application. Now Ying Dai and co-workers at Shandong University have predicted that single layers of vanadium disulphide and vanadium diselenide should be magnetic.

Dai and co-workers used density functional theory to predict the electronic and magnetic properties of these materials, which contain a hexagonal layer of V atoms sandwiched between two layers of S or Se atoms. According to their calculations, pristine monolayers of both materials exhibit ferromagnetic ordering, with both the V and the S or Se atoms carrying a small magnetic moment. Moreover, they find that the magnetic moments and the strength of the magnetic coupling in VS₂ and VSe₂ increase as the strain in the monolayer is increased from −5% to 5%.

The Shandong researchers report that a combination of through-bond and through-space interactions is responsible for the ferromagnetic behaviour they predict. However, they caution that the introduction of local defects and strains during the growth of real samples will complicate the experimental detection of ferromagnetism in monolayers of VS₂ and VSe₂.