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      Magnetization States of All-Oxide Spin Valves Controlled by Charge-orbital Ordering of Coupled Ferromagnets

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          Abstract

          Charge-orbital ordering is commonly present in complex transition metal oxides and offers interesting opportunities for novel electronic devices. In this work, we demonstrate for the first time that the magnetization states of the spin valve can be directly manipulated by charge-orbital ordering. We investigate the interlayer exchange coupling (IEC) between two epitaxial magnetite layers separated by a nonmagnetic epitaxial MgO dielectric. We find that the state of the charge-orbital ordering in magnetite defines the strength, and even the sign of the IEC. First-principles calculations further show that the charge-orbital ordering modifies the spin polarized electronic states at the Fe 3O 4/MgO interfaces and results in a sufficiently large phase shift of wave function which are responsible for the observed IEC sign change across Verwey temperature. Our findings may open new interesting avenues for the electric field control of the magnetization states of spin valves via charge-orbital ordering driven IEC sign change.

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          The emergence of spin electronics in data storage.

          Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.
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            Complexity in Strongly Correlated Electronic Systems

            A wide variety of experimental results and theoretical investigations in recent years have convincingly demonstrated that several transition metal oxides and other materials, have dominant states that are not spatially homogeneous. This occurs in cases in which several physical interactions -- spin, charge, lattice, and/or orbital -- are simultaneously active. This phenomenon causes interesting effects, such as colossal magnetoresistance, and it also appears crucial to understand the high temperature superconductors. The spontaneous emergence of electronic nanometer-scale structures in transition metal oxides, and the existence of many competing states, are properties often associated with complex matter where nonlinearities dominate, such as soft materials and biological systems. This electronic complexity could have potential consequences for applications of correlated electronic materials, because not only charge (semiconducting electronic), or charge and spin (spintronics) are of relevance, but in addition the lattice and orbital degrees of freedom are active, leading to giant responses to small perturbations. Moreover, several metallic and insulating phases compete, increasing the potential for novel behavior.
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              Spin-torque diode effect in magnetic tunnel junctions.

              There is currently much interest in the development of 'spintronic' devices, in which harnessing the spins of electrons (rather than just their charges) is anticipated to provide new functionalities that go beyond those possible with conventional electronic devices. One widely studied example of an effect that has its roots in the electron's spin degree of freedom is the torque exerted by a spin-polarized electric current on the spin moment of a nanometre-scale magnet. This torque causes the magnetic moment to rotate at potentially useful frequencies. Here we report a very different phenomenon that is also based on the interplay between spin dynamics and spin-dependent transport, and which arises from unusual diode behaviour. We show that the application of a small radio-frequency alternating current to a nanometre-scale magnetic tunnel junction can generate a measurable direct-current (d.c.) voltage across the device when the frequency is resonant with the spin oscillations that arise from the spin-torque effect: at resonance (which can be tuned by an external magnetic field), the structure exhibits different resistance states depending on the direction of the current. This behaviour is markedly different from that of a conventional semiconductor diode, and could form the basis of a nanometre-scale radio-frequency detector in telecommunication circuits.
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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                13 May 2013
                2013
                : 3
                : 1830
                Affiliations
                [1 ]CRANN, School of Physics, Trinity College , Dublin 2, Ireland
                [2 ]Department of Physics and MINT, University of Alabama , Tuscaloosa, AL 35487, USA
                [3 ]Ecole Polytechnique Federale de Lausanne/IPMC/LPMN , Station 3, CH 1015, Switzerland
                [4 ]King Saud University , Riyadh 11451, Saudi Arabia
                Author notes
                Article
                srep01830
                10.1038/srep01830
                3652083
                23665858
                bc3daabd-7f25-44c7-ae87-22f892db66bb
                Copyright © 2013, Macmillan Publishers Limited. All rights reserved

                This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/

                History
                : 16 January 2013
                : 18 April 2013
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