A high-temperature ferromagnetic topological insulating phase by proximity coupling

Abstract

Topological insulators are insulating materials that display conducting surface states protected by time-reversal symmetry, wherein electron spins are locked to their momentum. This unique property opens up new opportunities for creating next-generation electronic, spintronic and quantum computation devices. Introducing ferromagnetic order into a topological insulator system without compromising its distinctive quantum coherent features could lead to the realization of several predicted physical phenomena. In particular, achieving robust long-range magnetic order at the surface of the topological insulator at specific locations without introducing spin-scattering centres could open up new possibilities for devices. Here we use spin-polarized neutron reflectivity experiments to demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (EuS) to a topological insulator (Bi2Se3) in a bilayer system. This interfacial ferromagnetism persists up to room temperature, even though the ferromagnetic insulator is known to order ferromagnetically only at low temperatures (<17 K). The magnetism induced at the interface resulting from the large spin-orbit interaction and the spin-momentum locking of the topological insulator surface greatly enhances the magnetic ordering (Curie) temperature of this bilayer system. The ferromagnetism extends ~2 nm into the Bi2Se3 from the interface. Owing to the short-range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a topological insulator, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered topological insulator could allow efficient manipulation of the magnetization dynamics by an electric field, providing an energy-efficient topological control mechanism for future spin-based technologies.

Emergent functions of quantum materials

“…Concentrated magnetic elements are doped only in layers beneath the surfaces. As a matter of fact, the QAHE appears at a temperature as high as 2 K. To further enhance the stability of the QAHE, precise control of the Dirac point is required, along with high-quality heterostructures of pristine topological insulator and high-Curietemperature ferromagnets 111 .…”

Magnetic and magnetotransport properties of Bi2Se3 thin films doped by Eu

“…Although the properties of gapless interface states in the presence of magnetic impurities have been studied for more than 30 years ? , detailed investigation and explanation of the specific features of electron transport and of magnetic phenomena in 3D magnetic topological insulators remain an unresolved scientific problem even nowadays, being the subject of great interest 4,5 . We used Eu as magnetic impurity (J = 7/2) with the aim to study the effect of magnetic impurities on electron transport in 3D topological insulators.…”

Ferromagnetic and insulating behavior of LaCoO3 films grown on a (001) SrTiO3 substrate: A simple ionic picture explained ab initio

“…They are of extreme importance in the fabrication of spintronic devices. [5][6][7][8] Due to their technological relevance and rarity, it is interesting to explore and clarify the properties of one of such systems since this could help in designing other oxides with improved properties.…”