A spontaneous ferromagnetic moment can be induced in Bi₂Te₃ thin films below a temperature T≈16 K by the introduction of Mn dopants. We demonstrate that films grown via molecular beam epitaxy with the stoichiometry Mn_0.14Bi_1.86Te₃ maintain the crystal structure of pure Bi₂Te₃. The van der Waals nature of inter-layer forces in the Mn_0.14Bi_1.86Te₃ crystal causes lattice mismatch with the underlayer to have a limited effect on the resulting crystal structure, as we demonstrate by thin film growth on tetragonal MgF2 and the antiferromagnet NiF2 (110). Magnetic heterostructures consisting of Mn_0.14Bi_1.86Te₃ grown on thin film antiferromagnetic NiF₂ show magnetic behavior consistent with a coexistence of two decoupled magnetic layers. Electronic transport measurements in the Mn_0.14Bi_1.86Te₃ films exhibit the onset of the anomalous Hall effect at low temperatures. An inverse correlation between the magnitude of the anomalous Hall effect and the electron carrier density is observed in the samples. This correlation demonstrates that as the Fermi level is lowered and approaches the bulk band gap, the magnetic moment of the film increases, suggesting that topological surface states play a role in the development of ferromagnetism.

This article was published in Physical Review Materials and is available here.