Thickness and temperature dependence of the atomic-scale structure of SrRuO$_3$ thin films

TL;DR

This study investigates how the atomic-scale structure of SrRuO$_3$ thin films varies with thickness and temperature, revealing strong dependencies that influence their magnetic and electronic properties, including the observation of the Invar effect in ultrathin layers.

Contribution

It provides detailed insights into the temperature and thickness dependence of structural distortions in SrRuO$_3$ films, highlighting their impact on magnetic properties and the presence of the Invar effect in ultrathin layers.

Findings

Oxygen octahedral tilts depend on temperature, thickness, and interface distance.

Invar effect observed below ferromagnetic transition in layers as thin as 8 unit cells.

Structural distortions influence magnetic and transport properties.

Abstract

Due to the strong lattice-property relationships which exist in complex oxide epitaxial layers, their electronic and magnetic properties can be modulated by structural distortions induced at the atomic scale. The modification and control can be affected at coherent heterointerfaces by epitaxial strain imposed by the substrate or by structural modifications to accommodate the film-substrate symmetry mismatch. Often these act in conjunction with a strong dependence on the layer thickness, especially for ultrathin layers. Moreover, as a result of these effects, the temperature dependence of the structure may deviate largely from that of the bulk. The temperature-dependent structure of 3 to 44 unit cell thick ferromagnetic SrRuO$_3$ films grown on Nb-doped SrTiO$_3$ substrates are investigated using a combination of high-resolution synchrotron X-ray diffraction and high-resolution electron microscopy. This aims to shed light on the intriguing magnetic and magnetotransport properties of epitaxial SRO layers, subjected to extensive investigations lately. The oxygen octahedral tilts and rotations are found to be strongly dependent on the temperature, the film thickness, and the distance away from the film-substrate interface. As a striking manifestation of the coupling between magnetic order and lattice structure, the Invar effect is observed below the ferromagnetic transition temperature in epitaxial layers as thin as 8 unit cells, similar to bulk ferromagnetic SrRuO$_3$.