An original approach is proposed to study the magnetic phase separation phenomenon. It is based on the registration of the noise‐like FMR Fine Structure (FMR FS) caused by the magnetic interparticle dipole–dipole interaction between spatially separated ferromagnetic regions. Data obtained for a La0.7Pb0.3MnO3 single crystal point to the existence of spatially separated ferromagnetic regions. It is shown that FMR FS of the La0.7Pb0.3MnO3 single crystal is temperature reversible and disappears at the maximum of magnetoresistance.
Bulk polycrystalline La0.8Li0.2MnO3 is found to switch between a low‐resistance state and a high‐resistance state on thermal cycling. The low‐temperature, high‐resistance state exhibits strong electroresistance whereas the high‐temperature, low‐resistance state does not. The change in resistance between the two distinct states is of two orders of magnitude. It is proposed that the observed metastability may serve as the basis for resistive thermal‐switching devices.
Epitaxial thin films of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and charge‐ordered, antiferromagnetic Y0.5Ca0.5MnO3 (YCMO) were deposited on SrTiO3 (100) substrates by pulsed laser deposition (PLD). The heterostructure undergoes tetragonal distortion due to strong biaxial tensile strain imposed by the substrate. The LSMO–YCMO bilayers exhibit significant exchange bias (EB) across the interface even in a very small remnant magnetic field (～5 Oe) present in the superconductor magnet. The unidirectional exchange anisotropy at the interface can be switched by reversing the polarity of the remnant magnetic field.
The multiferroic Pb(Fe1/2V1/2)O3 (PFV) bulk ceramic was fabricated by a conventional ceramic sintering method. The strong visible‐light photovoltaic effect in Sn‐doped‐In2O3(ITO)/PFV/ITO structure capacitor was observed. The open‐circuit voltage was up to ～0.7 V, which was much higher than the value (～0.3 V) in BiFeO3 film. The photo‐excited electric current is almost proportional to the incident light illumination intensity. The good visible‐light photovoltaic makes PFV ceramic a potential candidate for practical application in solar cell devices.
We report the fabrication procedure and the characterization of an Al0.3Ga0.7As solar cell containing high‐density GaAs strain‐free quantum dots grown by droplet epitaxy. The production of photocurrent when two sub‐bandgap energy photons are absorbed simultaneously is demonstrated. The high quality of the quantum dot/barrier pair, allowed by the high quality of nanostructured strain‐free materials, opens new opportunities for quantum dot based solar cells.
We show, using Density Functional Theory (DFT) calculations, that compressed AgF2 should turn above 17 GPa into a layered narrow‐gap material with a huge intralayer antiferromagnetic (AFM) coupling constant, reminiscent of those seen for parent copper (II) oxides (e.g., La2CuO4). Compressed AgF2 is thus the first candidate for the non‐oxocuprate two‐dimensional antiferromagnet. Calculations indicate that AgF2 could subsequently be metallised above 38 GPa, likely giving rise to superconductivity (SC).
We propose a theory of thin film photovoltaics in which one of the polycrystalline films is made of a pyroelectric material grains such as CdS. That film is shown to generate strong polarization improving the device open circuit voltage. Implications and supporting facts for the major photovoltaic types based on CdTe and CuIn(Ga)Se2 absorber layers are discussed.
In this study, we report a low power Ni/GeOx /TiOy /TaN resistive random access memory (RRAM) using plasma‐modified electrode. The low sub‐mA switching current, highly uniform switching cycles (only 4% variation for the set) and good high‐temperature current distribution at 125 °C are simultaneously achieved in this RRAM device. Such good performance can be ascribed to interface plasma treatment on TaN electrode where the resulting Ta–N ionic bond increases the oxidation resistance and reduces the oxygen vacancy concentration near TaN interface that is favorable to lower switching power and improve high‐temperature current distribution.
Optically transparent and high‐quality hybrid ZnO nanoparticle and anthracene embedded polyphenylsiloxane (PPS) glass films were spin‐coated on quartz substrates. A strong Förster resonant energy transfer (FRET) process was indicated by the observation of quenching of the ZnO emission and an enhancement of the anthracene emission at room temperature. The efficiency of this energy transfer between ZnO and the S1 vibronic states of the anthracene molecules can be optimized to exceed 90%.
The superconducting current induced by the penetration of the long-range triplet component of superconducting correlations into a composite ferromagnetic interlayer has been detected in mesa-heterostructures based on oxide cuprate superconductors YBa2Cu3O7 ? δ and Au/Nb bilayer films with the composite oxide interlayer that is made of ferromagnetic films of manganite La0.7Sr0.3MnO3 and ruthenate SrRuO3 and has a thickness much larger than the length of correlations determined by the exchange field. The deviation of the superconducting current in the mesa-heterostructure with the fraction of the second harmonic of 13% from a sinusoidal current-phase relation has been detected; this deviation can also be due to the generation of the triplet component of superconducting correlations in the ferromagnet. 相似文献
The crystallization process of mechanically alloyed Fe75Zr25 metallic glasses is investigated by means of both thermo‐magnetization and in situ neutron powder thermo‐diffraction experiments in the temperature range 300–1073 K. It was found that the crystallization takes place in a two‐step process, involving firstly the appearance of metastable Fe and Fe2Zr crystalline phases between 880 K and 980 K, and a subsequent polymorphic transformation into Fe3Zr above 980 K. These findings explain the anomalous magnetization vs. temperature behaviour on heating–cooling cycles.
We study graphene growth on hafnia (HfO2) nanoparticles by chemical vapour deposition using optical microscopy, high resolution transmission electron microscopy and Raman spectroscopy. We find that monoclinic HfO2 nanoparticles neither reduce to a metal nor form a carbide while nucleating nanometer domain‐sized few layer graphene. Hence we regard this as an interesting non‐metallic catalyst model system with the potential to explore graphene growth directly on a (high‐k) dielectric.
We report a very simple and novel approach to produce anodic TiO2 nanotube arrays with highly defined and ordered tube openings. It is based on carrying out anodization through a slowly soluble photoresist coating. This eliminates the formation of undesired initiation layers on the tube tops and protects them to a certain extent from etching by the electrolyte.
Thin amorphous tantalum films are prepared on Si(111) substrates in a metallic glassy state. The amorphous monoatomic state of the film is characterized by X‐ray diffraction studies. The glassy state leads to a negative t emperature c oefficient of the r esistivity (TCR) for low sample temperatures <200 K which is attributed to incipient localization. Above 200 K a positive TCR is observed as expected for a normal Boltzmann transport regime. Upon heating the Si substrate to 1200 K TaSi2 is formed out of the amorphous tantalum film and the silicon substrate. The TaSi2 layer is crystalline as evident from X‐ray diffraction data.
Light‐induced degradation of charge carrier lifetime was observed in indium‐doped silicon. After defect formation, an annealing step at 200 °C for 10 min deactivates the defect and the initial charge carrier lifetime is fully recovered. The observed time range of the defect kinetics is similar to the well known defect kinetics of the light‐induced degradation in boron‐doped samples. Differences between defect formation in boron‐ and indium‐doped silicon are detected and discussed. A new model based on an acceptor self‐interstitial ASi–Sii defect is proposed and established with experimental findings and existing ab‐initio simulations.
Steady‐state and time‐resolved photoluminescence of silicon nanoparticles dispersed in low‐polar liquids at above room temperature is studied. The roles of low‐polar liquids as well as mechanisms responsible for their temperature‐dependent photoluminescence are discussed. The thermal sensitivity of the photoluminescence is estimated and application of the nanoparticles as nanothermometers is proposed.
The metastability of the bixbyite‐ and corundum‐type In2O3 polymorphs up to 33 GPa (at room temperature) is shown. While compressed (in diamond anvil cells) and laser‐heated, both polymorphs undergo a phase transition to the Rh2O3‐II‐type structure (space group Pbcn, No. 60). The direct transition from bixbyite to Rh2O3‐II structure has not yet been observed for any other oxide.
We report a stacked Y2O3/TiOx resistive random access memory (RRAM) device, showing good high‐temperature switching characteristics of extremely low reset current of 1 μA at 150 °C, large off/on resistance window (>200) at 150 °C, large rectification ratio of ～300 at 150 °C and good current distribution at 85 °C. The good rectifying property, lower high‐temperature sneak current and tighter high‐temperature current distribution can be attributed to the combined results of the oxygen vacancies in TiOx and the related carrier depletion effect.
We report enhanced anomalous photovoltaic effects and switchable photovoltage generation in pure and Pr–Cr co‐doped BiFeO3 (BFO) nanotubes (NTs). Influence of metal doping on short circuit current, open circuit voltage, power conversion efficiency and fill factor are investigated. The power conversion efficiency of pure BFO NTs (～0.207%) is found to be enhanced by several orders of magnitude in comparison with the reported bulk effect. Pr‐doped NTs provide highest values of power conversion efficiency (～0.5%).
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