Spin polarization of the two-dimensional electron gas at the EuO/SrTiO$_3$ interface

TL;DR

This study demonstrates that ultrathin EuO layers on SrTiO$_3$ induce a significant spin polarization in the 2DEG at the interface, with potential for spintronic applications in oxide electronics.

Contribution

It reveals that EuO induces spin polarization in the 2DEG at the EuO/SrTiO$_3$ interface starting from just two monolayers, supported by experimental and theoretical analysis.

Findings

Spin polarization occurs at EuO thickness of two monolayers.

Additional EuO layers enhance the magnetic Ti moment.

EuO/STO interface is promising for spintronic oxide devices.

Abstract

Spin-polarized two-dimensional electron gases (2DEGs) are of particular interest for functional oxide electronics applications. The redox-created 2DEG residing on the strontium titanate, SrTiO$_3$ (STO), side of a europium monoxide (EuO)/SrTiO$_3$ (001) interface is expected to be significantly spin-polarized due to the proximity to the strong ($7\,\mu_B/f.u.$) Heisenberg ferromagnet EuO. We apply magnetic circular dichroism in the angular distribution (MCDAD) of photoemitted electrons to investigate whether and how the induced spin polarization of the 2DEG depends on the dimensionality of the overlaying EuO layer. The experimental data are complemented by density functional theory calculations with a Hubbard $U$ term (DFT+$U$). We show that the EuO/STO interfacial 2DEG is spin-polarized even for ultrathin EuO overlayers, starting at an EuO threshold thickness of only two monolayers. Additional EuO monolayers even increase the induced magnetic Ti moment and thus the spin polarization of the 2DEG. Our results and the potential to enhance the magnetic order of EuO by other proximity effects indicate that the EuO/STO (001) interface is an ideal template for creating (multi-)functional spin-polarized 2DEGs for application in oxide electronics.