Electrically tuned magnetic order and magnetoresistance in a topological insulator

TL;DR

This study explores how electrical gating influences magnetic order and magnetoresistance in a ferromagnetic topological insulator, revealing complex MR behavior linked to magnetic tuning and topological effects, with implications for spintronic applications.

Contribution

It provides the first detailed experimental investigation of magnetoresistance evolution in a ferromagnetic topological insulator under electrical control, highlighting the interplay between magnetic order and topological surface states.

Findings

MR varies with Fermi level tuning, positive near Dirac point, negative at higher energies.

Magnetoresistance behavior is linked to competition between weak antilocalization and negative MR from magnetism.

Electrical control of magnetic order and MR opens pathways for TI-based spintronic devices.

Abstract

The Dirac-like surface states of the topological insulators (TIs) are protected by time reversal symmetry (TRS) and exhibit a host of novel properties. Introducing magnetism into TI, which breaks the TRS, is expected to create exotic topological magnetoelectric effects. A particularly intriguing phenomenon in this case is the magnetic field dependence of electrical resistance, or magnetoresistance (MR). The intricate interplay between topological protection and broken-TRS may lead to highly unconventional MR behaviour that can find unique applications in magnetic sensing and data storage. However, so far the MR of TI with spontaneously broken TRS is still poorly understood, mainly due to the lack of well-controlled experiments. In this work, we investigate the magneto transport properties of a ferromagnetic TI thin film fabricated into a field effect transistor device. We observe an unusually complex evolution of MR when the Fermi level (EF) is tuned across the Dirac point (DP) by gate voltage. In particular, MR tends to be positive when EF lies close to the DP but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture for localization, but is intimately correlated with the gate-tuned magnetic order. We show that the underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative MR. The simultaneous electrical control of magnetic order and magneto transport facilitates future TI-based spintronic devices.