Realization of Stable Ferromagnetic Order in Topological Insulator: Codoping Enhanced Magnetism in 4f Transition Metal Doped Bi2Se3

TL;DR

This study demonstrates that codoping with 4f transition metals like Eu and Sm in Bi2Se3 enhances stable ferromagnetic order, potentially enabling quantum anomalous Hall effect at higher temperatures.

Contribution

It introduces a novel codoping strategy with 4f transition metals to improve ferromagnetism and preserve insulating properties in topological insulators.

Findings

Eu and Sm favor Bi substitution with large magnetic moments

Codoping enhances ferromagnetic stability and insulating behavior

Findings facilitate realization of QAHE in TI systems

Abstract

The realization of long range and insulating ferromagnetic states in topological insulator (TI) has been a pressing issue since its discovery. Only recently, such state was achieved in Cr-doped Bi2-xSbxTe3, leading to the discovery of quantum anomalous Hall effect (QAHE). However, the effect is only observed at extremely low temperatures mainly due to the limited magnetism. To fully understand the mechanism of the ferromagnetic ordering whereby improving the ferromagnetism, we investigated 4f transition metal-doped Bi2Se3, using density-functional-theory approaches. We found that Eu and Sm prefer the Bi substitutional sites with large magnetic moments to ensure stable long-range ferromagnetic states. Additionally, codoping can be a novel strategy to preserve the insulating property of the host material as well as improving the incorporation of magnetic dopants. Our findings thus offer the critical step in facilitating the realization of QAHE in TI systems.