Search for enhanced magnetism at the interface between Bi$_2$Se$_3$ and EuSe

TL;DR

This study investigates the magnetic properties of the Bi$_2$Se$_3$/EuSe interface, finding no evidence of magnetic enhancement or remanent magnetization at low temperatures, thus contrasting with previous reports on similar heterostructures.

Contribution

The paper provides the first detailed magnetic characterization of the Bi$_2$Se$_3$/EuSe interface, demonstrating that it does not exhibit enhanced magnetism or increased Curie temperature.

Findings

No magnetic enhancement observed at the interface.

EuSe retains its bulk magnetic phase diagram at the interface.

Remanent magnetization is absent at temperatures down to 10 K.

Abstract

Enhanced magnetism has recently been reported for the topological-insulator/ferromagnet interface Bi$_2$Se$_3$/EuS with Curie temperatures claimed to be raised above room temperature from the bulk EuS value of 16 K. Here we investigate the analogous interface Bi$_2$Se$_3$/EuSe. EuSe is a low-temperature layered ferrimagnet that is particularly sensitive to external perturbations. We find that superconducting quantum interference device (SQUID) magnetometry of Bi$_2$Se$_3$/EuSe heterostructures reveals precisely the magnetic phase diagram known from EuSe, including the ferrimagnetic phase below 5 K, without any apparent changes from the bulk behavior. Choosing a temperature of 10 K to search for magnetic enhancement, we determine an upper limit for a possible magnetic coercive field of 3 mT. Using interface sensitive x-ray absorption spectroscopy we verify the magnetic divalent configuration of the Eu at the interface without contamination by Eu3+, and by x-ray magnetic circular dichroism (XMCD) we confirm at the interface the magnetic hysteresis obtained by SQUID. XMCD data obtained at 10 K in a magnetic field of 6 T indicate a magnetic spin moment of mz,spin = 7 $\mu$B/Eu$^{2+}$, in good agreement with the SQUID data and the expected theoretical moment of Eu2+. Subsequent XMCD measurements in zero field show, however, that sizable remanent magnetization is absent at the interface for temperatures down to about 10 K.