Electronic and Magnetic Properties of Small Co-O Quantum Wires
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1198-E04-09
Electronic and Magnetic Properties of Small Co-O Quantum Wires
Liudmila A. Pozhar1 and Constantine Mavromichalis2 Department of Physics and 2Department of Computer Science, University of Idaho,
1
POB 440903, Moscow, ID 85844-0903
ABSTRACT Electronic and magnetic properties of small Co-O atomic clusters (“quantum wires”) have been studied in the framework of the Hartree-Fock (HF) method. The obtained results indicate that non-stoichiometric Co - O molecules with more than two O atoms possess at least one remarkably stretchable O-O bond that may facilitate significant re-construction of such molecules to larger structures. This re-construction may result in energetically favorable spin realignment in “antiferromagnetic” HF singlet Co-O molecules converting the singlets to larger “ferromagnetic” HF triplets and pentets. Such a spin re-alignment is energetically favorable, and may happen at the antiferromagnet-ferromagnet interface in “critical” core (Co) – shell (CoO) exchange-biased nanoclusters, providing for minimization of the surface energy, and leading to a loss of exchange bias. The obtained results are in agreement with available experimental and computational data.
INTRODUCTION Electron spin states of exchange-biased, core (Co) – shell (Co-O) quantum dots and wires (QDs and QWs, respectively) satisfy major requirements applied to physical elements of quantum electronic systems that are expected to support integrated information storageprocessing, enable secure communications, and provide for a significant increase in efficacy and reliability of electronic devices and computational equipment of the future. In particular, typical electron spin relaxation time exceeding a nanosecond and reaching milliseconds has been experimentally observed for such systems [1]. A possibility to control single electron spins localized on an individual QD or QW has been demonstrated [2]. Exchange bias is one of physical phenomena that may be used to control electron spins necessary for electron spin-based quantum information processing in spintronics, quantum computing and communications. However, for realization of electron spin-based information processing scaling down the size of the QDs/QWs to only a few tens of atoms is required. This poses a question about the existence of exchange bias in such small QDs/QWs. Indeed, recent experimental observations [3] indicate that exchange bias disappears in core-shell Co/CoO nanoclusters of about several nanometers in size. Thus, understanding of physical mechanisms governing exchange bias phenomenon is necessary to establish conditions at which exchange bias may continue to exist in sub-critical size core-shell Co/CoO nanoclusters. In particular, sub-critical core-shell Co/CoO QDs and QWs synthesized in quantum confinement or on surfaces may possess the required structure, electronic and magnetic properties to support exchange bias.
While accurate experimental assessment of the necessary synthesis conditions, and properties of sub-critical size nanoclusters so synthe
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