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Nature. 2016 May 26;533(7604):513-6. doi: 10.1038/nature17635. Epub 2016 May 9.

A high-temperature ferromagnetic topological insulating phase by proximity coupling.

Author information

1
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
2
Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
3
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
4
Quantum Condensed Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
5
Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum, D-44801 Bochum, Germany.
6
Institute for Theoretical Solid State Physics, Institut fuer Festkoerper- und Werkstoffforschung, Dresden, D-01069 Dresden, Germany.
7
Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
8
Département de Physique, Ecole Normale Supérieure, Centre National de la Recherche Scientifique, Paris Sciences et Lettres Research University, Paris 75005, France.
9
Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 64, India.
10
Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.

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.

PMID:
27225124
DOI:
10.1038/nature17635

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