Spatially Confined Spin Polarization and magnetic sublattice control in (La,Sr)MnO3\u2212\u03b4 Thin Films by Oxygen Vacancy Ordering

Magnus Moreau,Sverre M Selbach,Thomas Tybell

doi:10.1038/s41598-017-04103-y

Magnus Moreau, Sverre M Selbach + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-04103-y

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Abstract

Perovskite oxides are known for their strong structure property coupling and functional properties such as ferromagntism, ferroelectricity and high temperature superconductivity. While the effect of ordered cation vacancies on functional properties have been much studied, the possibility of tuning the functionality through anion vacancy ordering has received much less attention. Oxygen vacancies in ferromagnetic La0.7Sr0.3MnO3−δ thin films have recently been shown to accumulate close to interfaces and form a brownmillerite structure (ABO2.5). This structure has alternating oxygen octahedral and tetrahedral layers along the stacking direction, making it a basis for a family of ordered anion defect controlled materials. We use density functional theory to study how structure and properties depend on oxygen stoichiometry, relying on a block-by-block approach by including additional octahedral layers in-between each tetrahedral layer. It is found that the magnetic and electronic structures follow the layers enforced by the ordered oxygen vacancies. This results in spatially confined electronic conduction in the octahedral layers, and decoupling of the magnetic sub-lattices in the octahedral and tetrahedral layers. These results demonstrate that anion defect engineering is a promising tool to tune the properties of functional oxides, adding a new avenue for developing functional oxide device technology.

Highlights

The ABO3 perovskite structure is prone to changes in stoichiometry, and recently there has been considerable interest in layered perovskite-derived structures like the Ruddlesden-Popper, Aurivillius and Dion-Jacobsen families with cation ordering[1,2,3]
An increasing number octahedral layers between the oxygen deficient tetrahedral layers is schematically shown in Fig. 1, where the oxygen stoichiometry can be controlled in a block-by-block approach, going from ABO2.5 with one octahedral and one tetrahedral layer superlattice (1:1), via
Before relying on a block-by-block approach to investigate the magnetism, we start by defining the stoichiometric ABO3.0 system and the (1:1) ABO2.5 oxygen deficient system

Summary

Introduction

The ABO3 perovskite structure is prone to changes in stoichiometry, and recently there has been considerable interest in layered perovskite-derived structures like the Ruddlesden-Popper, Aurivillius and Dion-Jacobsen families with cation ordering[1,2,3]. Combining spin polarization with 2-dimensional conductivity is interesting both on a fundamental level as well as for spintronic applications[10] Such realizations have been achieved in various superlattice configurations such as LaMnO3/SrMnO311–13, LaAlO3/SrMnO314, and SrTiO3/SrRuO315. While most of these studies have been on the ordering of cations and cation vacancies, anion vacancy ordering has recently been demonstrated as a route for altering the properties of thin films[16, 17]. Further it has been shown experimentally that it is possible to order anion vacancies in layers in thin films of ferromagnetic (La,Sr)MnO3−δ (LSMO), e.g. in a brownmillerite structure with ABO2.5 stoichiometry[18,19,20], making LSMO a model system for controlling functionality through anion ordering. A large electronic band gap and low dispersion in the tetrahedral layers results in electron confinement in the octahedral layers

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