Magnetic structure of GdBiPt: A candidate antiferromagnetic topological insulator

A topological insulator is a state of matter which does not break any symmetry and is characterized by topological invariants, the integer expectation values of nonlocal operators. Antiferromagnetism, on the other hand, is a broken symmetry state in which the translation symmetry is reduced and time reversal symmetry is broken. Can these two phenomena coexist in the same material? A proposal by Mong et al. [Phys. Rev. B 81, 245209 (2010)] asserts that the answer is yes. Moreover, it is theoretically possible that the onset of antiferromagnetism enables the nontrivial topology since it may create spin-orbit coupling effects which are absent in the nonmagnetic phase. The current work examines a real system, half-Heusler GdBiPt, as a candidate for topological antiferromagnetism. We find that the magnetic moments of the gadolinium atoms form ferromagnetic sheets which are stacked antiferromagnetically along the body diagonal. This magnetic structure may induce spin-orbit coupling on band electrons as they hop perpendicular to the ferromagnetic sheets.