Above 400 K Robust Perpendicular Ferromagnetic Phase in a Topological Insulator

TL;DR

This paper demonstrates a robust perpendicular ferromagnetic phase in a topological insulator at temperatures above 400 K, enabling the quantum anomalous Hall effect at unprecedented high temperatures for practical applications.

Contribution

The study introduces a method to significantly increase the Curie temperature of topological insulators by coupling them with a high-Tc magnetic insulator, achieving QAHE at over 400 K.

Findings

Curie temperature enhanced above 400 K

Surface states exhibit robust ferromagnetism

Surface is confirmed spin-polarized by spectroscopy

Abstract

The quantum anomalous Hall effect (QAHE) that emerges under broken time-reversal symmetry in topological insulators (TI) exhibits many fascinating physical properties for potential applications in nano-electronics and spintronics. However, in transition-metal doped TI, the only experimentally demonstrated QAHE system to date, the effect is lost at practically relevant temperatures. This constraint is imposed by the relatively low Curie temperature (Tc) and inherent spin disorder associated with the random magnetic dopants. Here we demonstrate drastically enhanced Tc by exchange coupling TI to Tm3Fe5O12, a high-Tc magnetic insulator with perpendicular magnetic anisotropy. Signatures that the TI surface states acquire robust ferromagnetism are revealed by distinct squared anomalous Hall hysteresis loops at 400 K. Point-contact Andreev reflection spectroscopy confirms that the TI surface is indeed spin-polarized. The greatly enhanced Tc, absence of spin disorder, and perpendicular anisotropy are all essential to the occurrence of the QAHE at high temperatures.