Bulk intergrowth of a topological insulator with a room-temperature ferromagnet

Abstract

We demonstrate that the layered room-temperature ferromagnet Fe 7Se 8 and the topological insulator Bi 2Se 3 form crystallographically oriented bulk composite intergrowth crystals. The morphology of the intergrowth in real space and reciprocal space is described. The basal planes of Bi 2Se 3 and Fe 7Se 8 are parallel in the micron-scale intergrowth, and hence the good cleavage inherent to the bulk phases is retained. Both phases in the intergrowth crystals display their intrinsic bulk properties: the ferromagnetism of the Fe 7Se 8 is anisotropic, with the magnetization easy axis in the plane of the crystals, and angle-resolved photoemission spectroscopy characterization shows that the topological surface states remain present on the Bi 2Se 3 and that a gap can be observed in the surface state dispersion. Crystals of nominal composition Bi 2-xFe xSe 3 are shown to be bulk intergrowths of the two phases Bi 2Se 3 and Fe 2Se 3. Significant solubility of Fe in Bi 2Se 3 is not observed. © 2012 American Physical Society.