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      Oxygen-vacancy tuning of magnetism in SrTi\(_{0.75}\)Fe\(_{0.125}\)Co\(_{0.125}\)O\(_{3-\delta}\) perovskite

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          Abstract

          We use density functional theory to calculate the structure, band-gap and magnetic properties of oxygen-deficient SrTi\(_{1-x-y}\)Fe\(_x\)Co\(_y\)O\(_{3-\delta}\) with x = y = 0.125 and \({\delta}\) = (0,0.125,0.25). The valence and the high or low spin-states of the Co and Fe ions, as well as the lattice distortion and the band-gap, depend on the oxygen deficiency, the locations of the vacancies, and on the direction of the Fe-Co axis. A charge redistribution that resembles a self-regulatory response lies behind the valence spin-state changes. Ferromagnetism dominates, and both the magnetization and the band gap are greatest at \({\delta}\) = 0.125. This qualitatively mimics the previously reported magnetization measured for SrTiFeO\(_{3-\delta}\), which was maximum at an intermediate deposition pressure of oxygen.

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          Periodic boundary conditions inab initiocalculations

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            Charge self-regulation upon changing the oxidation state of transition metals in insulators.

            Transition-metal atoms embedded in an ionic or semiconducting crystal can exist in various oxidation states that have distinct signatures in X-ray photoemission spectroscopy and 'ionic radii' which vary with the oxidation state of the atom. These oxidation states are often tacitly associated with a physical ionization of the transition-metal atoms--that is, a literal transfer of charge to or from the atoms. Physical models have been founded on this charge-transfer paradigm, but first-principles quantum mechanical calculations show only negligible changes in the local transition-metal charge as the oxidation state is altered. Here we explain this peculiar tendency of transition-metal atoms to maintain a constant local charge under external perturbations in terms of an inherent, homeostasis-like negative feedback. We show that signatures of oxidation states and multivalence--such as X-ray photoemission core-level shifts, ionic radii and variations in local magnetization--that have often been interpreted as literal charge transfer are instead a consequence of the negative-feedback charge regulation.
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              Physics of SrTiO3-based heterostructures and nanostructures: a review

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                Author and article information

                Journal
                12 July 2019
                Article
                10.1103/PhysRevMaterials.3.014404
                1907.05961
                b39fda7d-ed06-4cda-92c8-553dc96f59c3

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                Custom metadata
                Phys. Rev. Materials 3, 014404 (2019)
                11 pages, 10 figures
                cond-mat.mtrl-sci physics.app-ph physics.comp-ph

                Condensed matter,Technical & Applied physics,Mathematical & Computational physics

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