Surface states spread magnetism

Nature Commun. 5, 5349 (2014)

In topological insulators, such as Bi₂Te₃, the bulk does not conduct electricity, but there are electronic states at the surface that are highly conductive. These surface states are protected against impurities and passivation by topology, and their spin is locked at right angles to their momentum, which makes topological insulators promising for applications in spintronics. The interaction of surface states with magnetic atoms is a means of achieving control of the spin texture of topological insulators. However, such capabilities have remained elusive. Paolo Sessi and colleagues in Germany and Russia now report on the role of surface states in the emergence of magnetic order in Co- and Mn-doped Bi₂Te₃ samples.

In contrast to previous studies, which used non-local probes, the researchers used scanning tunnelling microscopy to monitor the electronic interaction between the surface states of the topological insulator and the magnetic adatoms deposited on top of it. They find that the surface state mediates the magnetic coupling among adatoms, resulting in the onset of ferromagnetic order for a low coverage of magnetic dopants and in the dependence of the magnetic anisotropy of the individual adatoms.