Impact of applied strain on the electron transport through ferroelectric tunnel junctions
ABSTRACT Combining nonequilibrium Green’s functions with density-functional theory, we have investigated the effect of external strain field on the tunneling electroresistance (TER) of ferroelectric material sandwiched between Pt electrodes. The results show that the strain induced para/ferroelectric phase transitions play an important role in the electronic transport properties of the junction. Sizable enhancements in the resistance are found for the strained ferroelectric junctions with a TER ratio of 9000%. Detail analyses show that the Ti–O displacements along the transport direction in ferroelectric barrier change the effective potential profile, resulting in a giant piezoelectric resistance in the ferroelectric tunnel junctions.
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ABSTRACT: The interplay between the electron transport in metal/ferroelectric/metal junctions with ultrathin ferroelectric barriers and the polarization state of a barrier is investigated. Using a model which takes into account screening of polarization charges in metallic electrodes and direct quantum tunneling across a ferroelectric barrier we calculate the change in the tunneling conductance associated with the polarization switching. We find the conductance change of a few orders of magnitude for metallic electrodes with significantly different screening lengths. This giant electroresistance effect is the consequence of a different potential profile seen by transport electrons for the two opposite polarization orientations. Comment: 4 pagesPhysical Review Letters 02/2005; · 7.73 Impact Factor
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ABSTRACT: Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes separated by a thin insulating barrier layer, are currently used in spintronic devices, such as magnetic sensors and magnetic random access memories. Recently, driven by demonstrations of ferroelectricity at the nanoscale, thin-film ferroelectric barriers were proposed to extend the functionality of MTJs. Due to the sensitivity of conductance to the magnetization alignment of the electrodes (tunneling magnetoresistance) and the polarization orientation in the ferroelectric barrier (tunneling electroresistance), these multiferroic tunnel junctions (MFTJs) may serve as four-state resistance devices. On the basis of first-principles calculations, we demonstrate four resistance states in SrRuO(3)/BaTiO(3)/SrRuO(3) MFTJs with asymmetric interfaces. We find that the resistance of such a MFTJ is significantly changed when the electric polarization of the barrier is reversed and/or when the magnetizations of the electrodes are switched from parallel to antiparallel. These results reveal the exciting prospects of MFTJs for application as multifunctional spintronic devices.Nano Letters 01/2009; 9(1):427-32. · 13.03 Impact Factor
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ABSTRACT: Using first-principles density functional calculations, we show that ferroelectricity can be induced in simple alkaline-earth-metal binary oxides such as barium oxide (BaO) using appropriate epitaxial strains. Going beyond the fundamental discovery, we highlight that the functional properties (polarization, dielectric constant, and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, making them of direct interest for applications. Finally, we show that magnetic binary oxides such as EuO, with the same rocksalt structure, behave similarly to the alkaline-earth-metal oxides, suggesting a route to new multiferroics combining ferroelectric and magnetic properties.Physical Review Letters 01/2010; 104(3):037601. · 7.73 Impact Factor