Strain driven monoclinic distortion of ultrathin CoO films in CoO/Pt(001) and exchange-coupled CoO/PtFe/Pt(001) systems

TL;DR

This study investigates how strain induces a monoclinic distortion in ultrathin CoO films grown on Pt(001) and PtFe/Pt(001), revealing structural changes and stable spin configurations at room temperature.

Contribution

It provides the first in situ, real-time surface x-ray diffraction analysis of strain-induced monoclinic distortion in ultrathin CoO films on different substrates.

Findings

Ultrathin CoO films grow epitaxially with a pseudo-cubic surface.

A monoclinic distortion occurs at room temperature due to anisotropic interfacial stress.

The distortion results in a c/a ratio greater than 1, stabilizing in-plane Co2+ spins.

Abstract

The structure and strain of ultrathin CoO films grown on a Pt(001) substrate and on a ferromagnetic PtFe pseudomorphic layer on Pt(001) have been determined with insitu and real time surface x-ray diffraction. The films grow epitaxially on both surfaces with an in-plane hexagonal pattern that yields a pseudo-cubic CoO(111) surface. A refined x-ray diffraction analysis reveals a slight monoclinic distortion at RT induced by the anisotropic stress at the interface. The tetragonal contribution to the distortion results in a ratio c/a > 1, opposite to that found in the low temperature bulk CoO phase. This distortion leads to a stable Co2+ spin configuration within the plane of the film.