Topological insulator interfaced with ferromagnetic insulators: Bi₂Te₃ thin films on magnetite and iron garnets

We have grown Bi₂Te₃ thin films on Y₃Fe₅O₁₂(111), Tm₃Fe₅O₁₂(111), Fe₃O₄(111), and Fe₃O₄(100) by molecular beam epitaxy with minimal chemical reaction at the interface. Electrical transport measurements were performed to study the magnetism induced by the proximity effect in the topological insulator in conjunction to the ferromagnetic insulators. We observed the anomalous Hall effect on these heterostructures. Magnetoresistance measurements at low temperature reveal a suppression of the weak antilocalization, indicating a possible topological surface state gap opening induced by the magnetic proximity effect. However, we did not observe any obvious x-ray magnetic circular dichroism (XMCD) on the Te M₄₅ edges. The results suggest that the ferromagnetism induced by the magnetic proximity effect via Van der Waals bonding in Bi₂Te₃ by is too weak to be detected by XMCD, but still can be observed by electrical transport measurements. This is consistent with published density-functional theory results on topological insulator/magnetic insulator heterostructure showing that only a small band gap of 9 meV is induced by the magnetic proximity effect.