Direct measurement of proximity-induced magnetism at the interface between a topological insulator and a ferromagnet

TL;DR

This study employs magnetic second harmonic generation to directly measure and characterize the induced magnetism at the interface between a topological insulator and a ferromagnet, revealing key magnetic properties and domain structures.

Contribution

It provides the first direct measurement of proximity-induced magnetism at the buried TI-ferromagnet interface using a novel optical technique.

Findings

Detected both in-plane and out-of-plane magnetizations at the interface.

Characterized magnetic domain structures at the TI surface.

Established a method for imaging magnetic domains at buried interfaces.

Abstract

When a topological insulator (TI) is in contact with a ferromagnet, both time reversal and inversion symmetries are broken at the interface. An energy gap is formed at the TI surface, and its electrons gain a net magnetic moment through short-range exchange interactions. Magnetic TIs can host various exotic quantum phenomena, such as massive Dirac fermions, Majorana fermions, the quantum anomalous Hall effect and chiral edge currents along the domain boundaries. However, selective measurement of induced magnetism at the buried interface has remained a challenge. Using magnetic second harmonic generation, we directly probe both the in-plane and out-of-plane magnetizations induced at the interface between the ferromagnetic insulator (FMI) EuS and the three-dimensional TI Bi2Se3. Our findings not only allow characterizing magnetism at the TI-FMI interface but also lay the groundwork for imaging magnetic domains and domain boundaries at the magnetic TI surfaces.