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Large Magnetoresistance in Fe3O4/4,4′-Bipyridine/Fe3O4 Organic Magnetic Tunnel Junctions C
- Sun, Meifang, Wang, Xiaocha, Mi, Wenbo
- Journal of physical chemistry 2018 v.122 no.5 pp. 3115-3122
- electrodes, electrons, geometry, iron, iron oxides, magnetism, physical chemistry
- Organic magnetic tunnel junctions (OMTJs) are promising systems thanks to their chemically tunable electronic property, long spin lifetime, and easy functionalizations. Here, the spin-dependent electronic transport properties in Fe₃O₄/4,4′-bipyridine/Fe₃O₄ OMTJs are investigated by first-principles quantum transport calculations. Since the transport properties of junctions are sensitive to device details, two types of terminations of Fe₃O₄ electrodes are considered. The device with tetrahedral Fe termination shows anomalous negative tunnel magnetoresistance (TMR), that is, which has a higher and lower junction resistance in the parallel and antiparallel magnetization configurations, respectively. When the contact termination is octahedral Fe, a large positive TMR of 180% appears. The difference in TMR sign of two OMTJs originates from the electrons transmission mediated by frontier molecular levels coupled differently to Fe d states. Furthermore, TMR can be effectively controlled by applied electrical bias by changing states of octahedral Fe involved in transport, which can reach 22000% at 0.1 V. Moreover, a perfect spin-filter effect is demonstrated irrespective of the contact geometry. The results contribute to a fundamental understanding of spin-dependent transport properties in OMTJs.