Tailoring epitaxial growth and magnetism in La1-xSrxMnO3 / SrTiO3 heterostructures via temperature-driven defect engineering

TL;DR

This study demonstrates how temperature-controlled defect engineering in La1-xSrxMnO3/SrTiO3 heterostructures can optimize structural and magnetic properties, crucial for spintronic applications, by balancing oxygen stoichiometry and impurity diffusion.

Contribution

It reveals the effects of growth temperature and annealing on defects and magnetism in LSMO/STO heterostructures, providing new strategies for high-quality ferromagnetic thin films.

Findings

Higher growth temperatures improve oxygen stoichiometry and magnetic properties.

Post-deposition annealing enables high-quality epitaxy at lower temperatures.

Impurity diffusion from SrTiO3 influences magnetic dead layer formation.

Abstract

Among the class of strongly-correlated oxides, La1-xSrxMnO3 $-$ a half metallic ferromagnet with a Curie temperature above room temperature $-$ has sparked a huge interest as a functional building block for memory storage and spintronic applications. In this respect, defect engineering has been in the focus of a long-standing quest for fabricating LSMO thin films with highest quality in terms of both structural and magnetic properties. Here, we discuss the correlation between structural defects, such as oxygen vacancies and impurity islands, and magnetism in La0.74Sr0.26MnO3/SrTiO3 (LSMO/STO) epitaxial heterostructures by systematic control of the growth temperature and post-deposition annealing conditions. Upon increasing the growth temperature within the 500 $-$ 700 $^{\circ}$C range, the epitaxial LSMO films experience a progressive improvement in oxygen stoichiometry, leading to enhanced magnetic characteristics. Concurrently, however, the use of a high growth temperature triggers the diffusion of impurities from the bulk of STO, which cause the creation of off-stoichiometric, dendritic-like SrMoOx islands at the film/substrate interface. As a valuable workaround, post-deposition annealing of the LSMO films grown at a relatively-low temperature of about 500 $^{\circ}$C permits to obtain high-quality epitaxy, atomically-flat surface as well as a sharp magnetic transition above room temperature and robust ferromagnetism. Furthermore, under such optimized fabrication conditions possible scenarios for the formation of the magnetic dead layer as a function of LSMO film thickness are discussed. Our findings offer effective routes to finely tailor the complex interplay between structural and magnetic properties of LSMO thin films via temperature-controlled defect engineering.