Colossal anisotropy in diluted magnetic topological insulators

We consider dilute magnetic doping in the surface of a three dimensional topological insulator where a two dimensional Dirac electron gas resides. We find that exchange coupling between magnetic atoms and the Dirac electrons has a strong and peculiar effect on both. First, the exchange-induced single ion magnetic anisotropy is very large and favors off-plane orientation. In the case of a ferromagnetically ordered phase, we find a colossal magnetic anisotropy energy, of the order of the critical temperature. Second, a persistent electronic current circulates around the magnetic atom and, in the case of a ferromagnetic phase, around the edges of the surface.

This work has been financially supported by MEC-Spain (Grant Nos MAT07-67845, FIS2010-21883-C02-01 and CONSOLIDER CSD2007-0010), by Proyecto de Iniciación en Investigación Fondecyt 11070008 and by Núcleo Científico Milenio “Magnetismo Básico y/o Aplicado” P06022-F. ASN acknowledges funding from Universidad de Alicante.