Magnetic proximity effect observed by interfacing ferrimagnets and topological insulators

After the first experimental realization of the quantum anomalous Hall effect in 2013, the challenge has been to repeat the feat at higher temperatures. One potential route toward achieving this is by utilizing the magnetic proximity effect. Through epitaxial growth, Pereira et al. demonstrated a method of achieving a topological gap opening, which is a characteristic signature of the proximity effect.

By using molecular beam epitaxy to grow the ferrimagnet Fe₃O₄, or magnetite, on the topological insulator Bi₂Te₃, and then the other way around, the authors were able to compare the chemical stability and crystalline quality of the two different approaches. They monitored the growth in real time and used X-ray photoelectron spectroscopy to characterize the structural quality of the film during every step.

Despite carefully optimizing the growth process, the group could not unambiguously determine the presence of the proximity effect in the first case. However, in the Bi₂Te₃-on-magnetite scenario, they observed competition between weak anti-localization and weak localization – indicative of a gap opening in the surface states at the layer interface.

“It is indeed surprising that we are able to grow heterostructures comprising a topological insulator and a magnetic layer in such a clean manner that we are able to obtain a satisfactory quality of the interface, and with that, we are able to experimentally realize some of the expected effects,” said author Vanda Pereira.

This work is a step toward creating chemically clean interfaces for studying the magnetic proximity effect at high temperatures. Though these structures have potential spintronic applications, significant advances in their preparation and fundamental understanding is still needed prior to these applications.

Source: “Interfacing topological insulators and ferrimagnets: Bi₂Te₃ and Fe₃O₄ heterostructures grown by molecular beam epitaxy,” by V. M. Pereira, C. N. Wu, C.-A. Knight, A. Choa, L.H. Tjeng, and S. G. Altendorf, APL Materials (2020). The article can be accessed at https://doi.org/10.1063/5.0010339 .