Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO3(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO3/Pt junctions with a sub-μm Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ∼30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO3/Pt (Cr/BaTiO3) interface +0.42(−0.03) eV following downward to upward polarization reversal.
Gaynutdinov, R.; Minnekaev, M.; Mitko, S.; Tolstikhina, A.; Zenkevich, A.; Ducharme, Stephen; and Fridkin, V., "Polarization switching kinetics in ultrathin ferroelectric barium titanate film" (2013 b s t r a c tThe investigation of polarization switching kinetics in an ultrathin barium titanate film reveals true threshold switching at a large coercive electric field, evidence that switching is of intrinsic thermodynamic nature, rather than of extrinsic nature initiated by thermal nucleation, which has no true threshold field. The switching speed of a 7 nm thick epitaxial film exhibits a critical slowing as the threshold is approached from above, a key characteristic of intrinsic switching. In contrast, a bulk crystal exhibits nucleation-initiated switching, which has no threshold, and proceeds even at fields well below the nominal coercive field, which was determined independently from the polarization-electric field hysteresis loop. Previously, this phenomenon was only reported for ultrathin ferroelectric polymer Langmuir-Blodgett films. Since both the thermodynamic coercive field and the intrinsic switching kinetics are derived from the mean field theory of ferroelectricity, we expect that these phenomena will be found in other ferroelectric films at the nanoscale.
Ultrathin BaTiO3/Fe bi-layers were synthesized on MgO(001) and SrTiO3(001) substrates by pulsed laser deposition in a single vacuum cycle. The full electronic band structure at the Fe/BaTiO3 interface has been determined by hard x-ray photoemission spectroscopy measurements. Depending on the growth conditions, the valence and conduction band offsets are found 3.05–3.26 eV and 0.9–1.2 eV, respectively. Interface sensitive conversion electron Mößbauer spectroscopy demonstrates the absence of any magnetically dead layer thus proving that the determined band alignment is related to a sharp Fe/BaTiO3 interface structure down to the atomic scale.
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