81 research outputs found
Lattice structure and magnetization of LaCoO3 thin films
We investigate the structure and magnetic properties of thin films of the
LaCoO compound. Thin films are deposited by pulsed laser deposition on
various substrates in order to tune the strain from compressive to tensile.
Single-phase (001) oriented LaCoO layers were grown on all substrates
despite large misfits. The tetragonal distortion of the films covers a wide
range from -2% to 2.8%. Our LaCoO films are ferromagnetic with Curie
temperature around 85 K, contrary to the bulk. The total magnetic moment is
below /Co, a value relatively small for an exited spin-state
of the Co ions, but comparable to values reported in literature. A
correlation of strain states and magnetic moment of Co ions in
LaCoO thin films is observed.Comment: submitted tu European Phys. J.
Strain-induced insulator state in La_0.7Sr_0.3CoO_3
We report on the observation of a strain-induced insulator state in
ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to
enhance the resistivity by several orders of magnitude. Reversible strain of
0.15% applied using a piezoelectric substrate triggers huge resistance
modulations, including a change by a factor of 10 in the paramagnetic regime at
300 K. However, below the ferromagnetic ordering temperature, the magnetization
data indicate weak dependence on strain for the spin state of the Co ions. We
interpret the changes observed in the transport properties in terms of a
strain-induced splitting of the Co e_g levels and reduced double exchange,
combined with a percolation-type conduction in an electronic cluster state
Reversible strain effect on the magnetization of LaCoO3 films
The magnetization of ferromagnetic LaCoO3 films grown epitaxially on
piezoelectric substrates has been found to systematically decrease with the
reduction of tensile strain. The magnetization change induced by the reversible
strain variation reveals an increase of the Co magnetic moment with tensile
strain. The biaxial strain dependence of the Curie temperature is estimated to
be below 4K/% in the as-grown tensile strain state of our films. This is in
agreement with results from statically strained films on various substrates
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Strain-controlled switching kinetics of epitaxial PbZr0.52Ti0.48O3 films
We investigate the effect of biaxial strain on the switching of ferroelectric thin films. The strain state of epitaxial PbZr0.52Ti0.48O3 films is controlled directly and reversibly by the use of piezoelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (001) substrates. At small external electric fields, the films show switching characteristics consistent with a creep-like domain wall motion. In this regime, we find a huge decrease of the switching time under compressive strain. For larger external electric fields, the domain wall motion is in a depinning regime. The effect of compressive strain is more moderate in this region and shows a reduction in the switching kinetics
Thickness-dependent Ru exchange spring at La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub>âSrRuO<sub>3</sub> interface
The conducting oxide ferromagnets SrRuO3 (SRO) and LaSr0.3MnO3 (LSMO) form a Ru exchange spring at a coherent lowâinterdiffusion interface grown on TiO2âterminated SrTiO3(STO)(001) substrates as SRO(d)/LSMO/STO(001) bilayers. Fieldâ and temperatureâdependent magnetization data with systematically varied thickness d of SRO from 7 to 18 unit cells (uc) indicate a thickness of 10â14 uc of the exchange spring which governs magnetic switching and causes thicknessâdependent fieldâcooling effects. Mn L3 edge Xâray magnetic circular dichroism (XMCD) data reveal the dominating inâplane orientation of interfacial spins. In low magnetic fields, noncoplanar, topologically nontrivial spin textures arise and can be switched, driven by the Zeeman energy of the LSMO layer
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The Copernicus surface velocity platform drifter with barometer and reference sensor for temperature (SVP-BRST): genesis, design, and initial results
To support calibration and validation of satel- lite sea surface temperature (SST) retrievals, over 60 high- resolution SST (HRSST) drifting buoys were deployed at sea between 2012 and 2017. Their data record is reviewed here. It is confirmed that sea state and immersion depth play an important role in understanding the data collected by such buoys and that the SST sensors need adequate insu- lation. In addition, calibration verification of three recovered drifters suggests that the sensor drift is low, albeit negative at around â0.01 K yearâ1. However, the statistical significance of these results is limited, and the calibration procedure could not be exactly reproduced, introducing additional uncertain- ties into this drift assessment. Based on lessons learnt from these initial buoys, a new sensor package for the Surface Velocity Platform with Barometer (SVP-B) was designed to serve calibration of SST retrievals by European Unionâs Copernicus satellites. The novel sensor package includes an HRSST sensor calibrated by a metrology laboratory. The sensor includes a pressure probe to monitor immersion depth in calm water and acquires SST data at 1 Hz over a 5 min in-
terval every hour. This enables the derivation of mean SST as well as several percentiles of the SST distribution. The HRSST sensor is calibrated with an uncertainty better than 0.01 K. Analysis of the data collected by two prototypes de- ployed in the Mediterranean Sea shows that the buoys are able to capture small-scale SST variations. These variations are found to be smaller when the sea state is well mixed and when the buoys are located within eddy cores. This affects the drifter SST data representativeness, which is an aspect of importance for optimal use of these data
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Binding energy referencing for XPS in Alkali metal-based battery materials research (II): Application to complex composite electrodes
X-ray photoelectron spectroscopy (XPS) is a key method for studying (electro-)chemical changes in metal-ion battery electrode materials. In a recent publication, we pointed out a conflict in binding energy (BE) scale referencing at alkali metal samples, which is manifested in systematic deviations of the BEs up to several eV due to a specific interaction between the highly reactive alkali metal in contact with non-conducting surrounding species. The consequences of this phenomenon for XPS data interpretation are discussed in the present manuscript. Investigations of phenomena at surface-electrolyte interphase regions for a wide range of materials for both lithium and sodium-based applications are explained, ranging from oxide-based cathode materials via alloys and carbon-based anodes including appropriate reference chemicals. Depending on material class and alkaline content, specific solutions are proposed for choosing the correct reference BE to accurately define the BE scale. In conclusion, the different approaches for the use of reference elements, such as aliphatic carbon, implanted noble gas or surface metals, partially lack practicability and can lead to misinterpretation for application in battery materials. Thus, this manuscript provides exemplary alternative solutions
Standardization of Marine Meteorological Data from FINO Offshore Platforms
KlimawandelDer Ausbau der Offshore-Windenergie gehört zu den erklĂ€rten Zielen der Bundesregierung. Um bessere Ken ntnisse der Bedingungen auf See zu erlangen, wurden drei Forschungsplattformen in der Nordsee (FINO 1 und 3) und Ostsee (FINO 2) errichtet. An diesen werden meteorologische und ozeanographische GröĂen in unterschiedlichen Höhen gemessen, um unter anderem Aussagen zu Vertikalprofilen der Windgeschwindigkeit treffen zu können. Da sich die Plattformen und Masten im Design unterscheiden und sich insbesondere bei den Windmessungen deutlich ein richtungsabhĂ€ngiger Einfluss auf die Messungen zeigt, ist fĂŒr die Vergleichbarkeit der Standorte eine standardisierte Auswertung der Messergebnisse erforderlich. Ziel des Projektes FINO-Wind ist es, die Vergleichbarkeit der Daten der drei Standorte zu verbessern und den Datennutzern nach standardisierten Methoden qualitĂ€tsgeprĂŒfte Daten zur VerfĂŒgung zu stellen. Es sollen deshalb Standardisierungsverfahren zur Auswertung der Winddaten entwickelt werden. Insbesondere die verschiedenen Masteffekte werden eingehend untersucht und durch Windkanalmessungen, Vergleich mit LiDAR-Daten, CFD (Computational Fluid Dynamics)-Modellierungen und Anwendung der UAM (Uniform ambient flow mast correction)-Methode abgeschĂ€tzt. Daraus werden Korrekturfaktoren fĂŒr Windmessungen abgeleitet, die spĂ€ter angewendet werden sollen. Die Messdaten, die als 10-Minuten-Werte vorliegen, werden des Weiteren einer umfassenden und automatisierten QualitĂ€tsprĂŒfung unterzogen. Dabei durchlaufen die Daten in aufeinanderfolgenden Schritten formale, klimatologische, zeitliche, Wiederholungs- und KonsistenzprĂŒfungen und werden nach erfolgreichem Abschluss jeder Sequenz mit spezifischen QualitĂ€tsflags gekennzeichnet. Aus der Analyse und dem Vergleich der Instrumentierung in unterschiedlichen Höhen, der Installation und Ausrichtung sowie die Mastkonstruktionen sollen Empfehlungen herausgearbeitet werden, wie zukĂŒnftige Anwendungen im Bereich der Offshore-Windmessungen verbessert werden können
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