What drives the insulating state in ultrathin films of SrRuO3?

TL;DR

This study uses density functional calculations to explore how the electronic and magnetic properties of ultrathin SrRuO3 films on SrTiO3 substrates evolve with thickness, revealing complex magnetic states and coexistence of phases.

Contribution

It uncovers the coexistence of antiferromagnetic insulating and metallic solutions in ultrathin SrRuO3 films, highlighting unusual magnetic behavior that persists with increasing thickness.

Findings

Ultrathin films are at the brink of a spin-state transition to an antiferromagnetic insulator.

Two solutions coexist at four monolayers: antiferromagnetic insulator and a metallic phase.

Surface remains antiferromagnetic while the bulk becomes ferromagnetic in thicker films.

Abstract

Using density functional calculations we have examined the evolution of the electronic structure of SrRuO3 films grown on SrTiO3 substrates as a function of film thickness. At the ultrathin limit of two monolayers (RuO2-terminated surface) the films are found to be at the brink of a spin-state transition which drives the system to an antiferromagnetic and insulating state. Increasing the film thickness to four monolayers, one finds the surprising result that two entirely different solutions coexist. An antiferromagnetic insulating solution coexists with a metallic solution corresponding to an antiferromagnetic surface and a ferromagnetic bulk. The electronic structure found at the ultrathin limit persists for thicker films and an unusual result is predicted. Thicker films are found to be metallic as expected for the bulk, but the magnetism does not directly evolve to the bulk ferromagnetic state. The surface remains antiferromagnetic while the bulk exhibits ferromagnetic ordering.