1,720,965 research outputs found
Bandwidth-limited control of orbital and magnetic orders in half-doped manganites by epitaxial strain
No full textThe magnetotransport phase diagram of half-doped manganites Ln0.5A0.5MnO3 (Ln=La3+, Nd3+, etc., and A=Sr2+, Ca2+, etc.) is primarily dictated by the bare conduction bandwith (W0), which itself is controlled by the Mn-O-Mn bond angle, and the carrier concentration. In thin films, epitaxial strain (ε) provides an additional tool to tune W0 by selecting orbital ordering at fixed carrier concentration. Here, we will show that compressive or tensile epitaxial strain on half-doped manganites can have a tremendous and distinct effect on La0.5Sr0.5MnO3 (LSMO5) and La0.5Ca0.5MnO3 (LCMO5), having broad or narrow W0, respectively. It is found that in LSMO5, large compressive strain triggers a change from a ferromagnetic and metallic ground state to an insulating and antiferromagnetic state whereas a tensile strain produces an antiferromagnetic but metallic state. In contrast, under strain, LCMO5 remains an antiferromagnetic insulator irrespectively of the strain state. These results illustrate that orbital ordering largely depends on the interplay between W0 and ε and provide a guideline towards responsive manganite layers
Correlation between growth dynamics and dielectric properties of epitaxial BaTiO3 films
No full textWe report on the effect of the substrate temperature on the growth dynamics and dielectric
properties of BaTiO3 epitaxial films on Nb:SrTiO3 (001) substrates. By real-time reflection high
energy electron diffraction analysis, we quantitatively estimated the adatoms surface diffusivity as
a function of temperature. The increase of the substrate temperature promotes surface diffusion,
which reflects in the improvement of BaTiO3 ferroelectric properties up to 680 C. Above this
temperature, Ba re-evaporation occurs, leading to a rapid deterioration of the dielectric and
ferroelectric properties. This work shed light on thermally activated physical mechanisms which
determine the ferroelectric properties of BaTiO3 films
Absence of strain-mediated magnetoelectric coupling at fully epitaxial Fe/BaTiO3 interface (invited)
Full text linkInterfacial MagnetoElectric coupling (MEC) at ferroelectric/ferromagnetic interfaces has recently emerged as a promising route to achieve electrical writing of magnetic information in spintronic devices. For the prototypical Fe/BaTiO3 (BTO) system, various MEC mechanisms have been theoretically predicted. Experimentally, it is well established that using BTO single crystal substrates MEC is dominated by strain-mediated mechanisms. In case of ferromagnetic layers epitaxially grown onto BTO films, instead, no direct evidence for MEC has been provided, apart from the results obtained on tunneling junction sandwiching a BTO tunneling barrier. In this paper, MEC at fully epitaxial Fe/BTO interface is investigated by Magneto-Optical Kerr Effect and magnetoresistance measurements on magnetic tunnel junctions fabricated on BTO. We find no evidence for strain-mediated MEC mechanisms in epitaxial systems, likely due to clamping of BTO to the substrate. Our results indicate that pure electronic MEC is the route of choice to be explored for achieving the electrical writing of information in epitaxial ferromagnet-ferroelectric heterostructures
Electric field control of magnetic properties and electron transport in BaTiO3-based multiferroic heterostructures
Full text linkIn this paper, we report on a purely electric mechanism for achieving the electric control of the interfacial spin polarization and magnetoresistance in multiferroic tunneling junctions. We investigate micrometric devices based on the Co/Fe/BaTiO3/La0.7Sr0.3MnO3 heterostructure, where Co/Fe and La0.7Sr0.3MnO3 are the magnetic electrodes and BaTiO3 acts both as a ferroelectric element and tunneling barrier. We show that, at 20 K, devices with a 2 nm thick BaTiO3 barrier present both tunneling electroresistance (TER = 12 ± 0.1%) and tunneling magnetoresistance (TMR). The latter depends on the direction of the BaTiO3 polarization, displaying a sizable change of the TMR from -0.32 ± 0.05% for the polarization pointing towards Fe, to -0.12 ± 0.05% for the opposite direction. This is consistent with the on-off switching of the Fe magnetization at the Fe/BaTiO3 interface, driven by the BaTiO3 polarization, we have previously demonstrated in x-ray magnetic circular dichroism experiments
Selecting Steady and Transient Photocurrent Response in BaTiO3 Films
Full text linkThe ferroelectric polarization and short-circuit photocurrent in BaTiO3 thin films are studied for different contact configurations that allow to measure the photoresponse and polarization under the presence of large or negligible imprint field. It is found that in all cases, the direction of the photocurrent is dictated by the depolarizing field and ultimately by the film polarization, with a negligible contribution of the imprint electric field. However, dramatic differences are found in their time-dependent photoresponse. Whereas in presence of imprint, steady photocurrents are observed under suitable illumination, transient photocurrents are generated in absence of imprint. It is argued that this distinct behavior is determined by the different Schottky barrier height at electrodes which thus offers a simple way to tune the film photoresponse. These findings can be exploited for electro-optic read-out and writing of ferroelectric memories
Large room-temperature electroresistance in dual-modulated ferroelectric tunnel barriers
Full text linkPt/BaTiO3/La0.7Sr0.3MnO3 tunnel junctions, at negative voltage bias, for two polarization directions are represented. It is demonstrated that reversing the polarization direction of a ferroelectric barrier in a tunnel junction leads to a change of junction conductance and capacitance, with concomitant variations on the barrier height and effective thickness, both contributing to produce larger electroresistance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Two dimensional growth of ultrathin Fe films on BaTiO3 with sharp chemical interface
Full text linkThe Fe/BaTiO3 interface is a prototypical artificial multiferroic system displaying purely electronic magnetoelectric effects at room temperature. As magneto-electric coupling is essentially localized at the interface, the properties of the very first Fe layers in contact with BaTiO3 play a major role.
In this paper, we investigate, by using X-ray photoemission spectroscopy and photoelectron diffraction, the in-situ growth, by molecular beam epitaxy, of ultrathin Fe films (7 monolayers) on a BaTiO3/SrTiO3(001) template. We found that growing the Fe films above room temperature (373 K) is essential in order to avoid island growth and obtain a continuous film. Post-annealing up to 473K improves the film crystallinity but prevents chemical interdiffusion and roughening. Just an interfacial monolayer of oxidized iron is detected in these conditions, which appears as an unavoidable consequence of the Fe/BaTiO3 chemical interaction. Its active role in magnetoelectric coupling must be carefully taken into account to correlate theoretical predictions and experiments
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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