Fundamental thickness limit of itinerant ferromagnetic SrRuO$_3$ thin films

TL;DR

This study investigates the fundamental thickness limit of ferromagnetism in SrRuO$_3$ thin films, revealing that quantum confinement effects reduce Curie temperature and eventually suppress ferromagnetism at very thin layers.

Contribution

It identifies the orbital-selective quantum confinement as the cause of the ferromagnetic thickness limit in SrRuO$_3$ films, combining experimental results with theoretical modeling.

Findings

SrRuO$_3$ remains metallic down to 2 unit cells

Curie temperature decreases with decreasing thickness

Ferromagnetism vanishes at 2 unit cells due to reduced density of states

Abstract

We report on a fundamental thickness limit of the itinerant ferromagnetic oxide SrRuO$_3$ that might arise from the orbital-selective quantum confinement effects. Experimentally, SrRuO$_3$ films remain metallic even for a thickness of 2 unit cells (uc), but the Curie temperature, T$_C$, starts to decrease at 4 uc and becomes zero at 2 uc. Using the Stoner model, we attributed the T$_C$ decrease to a decrease in the density of states (N$_o$). Namely, in the thin film geometry, the hybridized Ru-d$_yz,zx$ orbitals are terminated by top and bottom interfaces, resulting in quantum confinement and reduction of N$_o$.