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

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.

Structural Phase Transitions to 2D and 3D Oxygen Vacancy Patterns in a Perovskite Film Induced by Electrical and Mechanical Nanoprobing

“…We find that the alternate stacking of octahedral and tetrahedral layers in the BM phase produces A-type antiferromagnetism under compressive perpendicular strain (Table S2, Supporting Information). This result agrees with a previous report on LSMO/ STO, [11] which also revealed that spins in the octahedral and tetrahedral layers order parallel and antiparallel, respectively. The calculated distributions of Mn magnetic moments shown in Figure S6, Supporting Information, displaying distinctive peaks at 3.70 μ B and 4.35 μ B , confirm the existence of two magnetic sub-lattices.…”

“…The physical properties of ABO 3 perovskites alter drastically with the BOB bond lengths and bond angles through a changing degree of overlap between the d orbitals of the B-site cations and the p orbitals of the oxygen anions. Distortions and rotations of oxygen octahedra, often designed by heteroepitaxial growth, [37,38] have been shown to change the electronic structure, to produce electronic and magnetic anisotropies, [11,[39][40][41] and to stabilize ferroelectricity. [42,43] In this work, we demonstrate how migration and reordering of oxygen vacancies during simultaneous voltage pulsing and local mechanical straining produces a complex pattern of distorted oxygen tetrahedra, pentahedra, and octahedra in an epitaxial LSMO film.…”

“…Active tuning of the oxygen stoichiometry through the migration of oxygen vacancies can radically alter the electrical resistivity, [1][2][3][4][5][6][7] magnetization state, [5,6,[8][9][10][11] and optical transparency [8] of perovskite oxides. Of particular technological interest are controlled property changes induced by small voltages, enabling low-power memory, [1,2] neuromorphic computing, [12,13] and other switchable Oxygen vacancy migration and ordering in perovskite oxides enable manipulation of material properties through changes in the cation oxidation state and the crystal lattice.…”

Reversible Hydrogen-Induced Phase Transformations in La0.7Sr0.3MnO3 Thin Films Characterized by In Situ Neutron Reflectometry

“…17,26 The lattice distortion and symmetry breaking cause redistribution of the t 2g and e g orbital populations that facilitates the tunability of a wide range of physical properties. 17,23 The evolution of the structural transformation during hydrogenation at a fixed temperature was measured by in situ XRD. The two-dimensional plot of the XRD intensity as a function of the angle of incidence in Figure 2a shows the evolution of the structural transformation during hydrogenation at 300 °C.…”

“…22 The orbital and spin states in manganites are easily tunable by symmetry breaking or lattice distortion driven by strain 23 and the emergence of cooperative charge and orbital ordering phenomena are found to correlate with structural transformations resulting in order−disorder transitions from changes in charge, spin, orbital, and lattice DOFs. 9,17,23,24 The poor understanding of the fundamental mechanisms of hydrogenation and the lack of systematic studies of the hydrogenation process are related to the difficult detection of hydrogen, or protons, primarily because of their size and lightweight. 7 The first step toward understanding the atomic mechanisms of hydrogen-induced transformations is the quantification of the amount and the distribution of hydrogen throughout the lattice.…”