Surface state mediated ferromagnetism in Mn0.14Bi1.86Te3 thin films

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 Mn0.14Bi1.86Te3 maintain the crystal structure of pure Bi2Te3. The van der Waals nature of inter-layer forces in the Mn0.14Bi1.86Te3 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 Mn0.14Bi1.86Te3 grown on thin film antiferromagnetic NiF2 show magnetic behavior consistent with a coexistence of two decoupled magnetic layers. Electronic transport measurements in the Mn0.14Bi1.86Te3 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.