184 research outputs found
Quantum Phase Transition in Pr2CuO4 to Collinear Spin State in Inclined Magnetic Field: A Neutron Diffraction Observation
In the external field slightly inclined to the - or y-axis of the
frustrated tetragonal atiferromagnet Pr2CuO4, a transition is discovered from
the phase with orthogonal antiferromagnetic spin subsystems along [1,0,0] and
[0,1,0] to the phase with the collinear spins. This phase is shown to be due to
the pseudodipolar interaction, and transforms into the spin-flop phase S perp H
asymptotically at very high field. The discovered phase transition holds at T=0
and is a quantum one, with the transition field being the critical point and
the angle between two subsystems being the order parameter
The de Haas-van Alphen effect across the metamagnetic transition in SrRuO
We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant
metamagnet SrRuO. Extremely high sample purity allows the
observation of dHvA oscillations both above and below the metamagnetic
transition field of 7.9 T. The quasiparticle masses are fairly large away from
the transition, and are enhanced by up to an extra factor of three as the
transition is approached, but the Fermi surface topography change is quite
small. The results are qualitatively consistent with a field-induced Stoner
transition in which the mass enhancement is the result of critical
fluctuations.Comment: 4 pages, 3 figure
The balancing act between high electronic and low ionic transport influenced by perovskite grain boundaries
\ua9 2024 The Royal Society of Chemistry.A better understanding of the materials\u27 fundamental physical processes is necessary to push hybrid perovskite photovoltaic devices towards their theoretical limits. The role of the perovskite grain boundaries is essential to optimise the system thoroughly. The influence of the perovskite grain size and crystal orientation on physical properties and their resulting photovoltaic performance is examined. We develop a novel, straightforward synthesis approach that yields crystals of a similar size but allows the tuning of their orientation to either the (200) or (002) facet alignment parallel to the substrate by manipulating dimethyl sulfoxide (DMSO) and tetrahydrothiophene-1-oxide (THTO) ratios. This decouples crystal orientation from grain size, allowing the study of charge carrier mobility, found to be improved with larger grain sizes, highlighting the importance of minimising crystal disorder to achieve efficient devices. However, devices incorporating crystals with the (200) facet exhibit an s-shape in the current density-voltage curve when standard scan rates are used, which typically signals an energetic interfacial barrier. Using the drift-diffusion simulations, we attribute this to slower-moving ions (mobility of 0.37
7 10-10 cm2 V-1 s-1) in combination with a lower density of mobile ions. This counterintuitive result highlights that reducing ion migration does not necessarily minimise hysteresis
Gravimetric and density profiling using the combination of surface acoustic waves and neutron reflectivity
A new approach is described herein, where neutron reflectivity measurements that probe changes in the density profile of thin films as they absorb material from the gas phase have been combined with a Love wave based gravimetric assay that measures the mass of absorbed material. This combination of techniques not only determines the spatial distribution of absorbed molecules, but also reveals the amount of void space within the thin film (a quantity that can be difficult to assess using neutron reflectivity measurements alone). The uptake of organic solvent vapours into spun cast films of polystyrene has been used as a model system with a view to this method having the potential for extension to the study of other systems. These could include, for example, humidity sensors, hydrogel swelling, biomolecule adsorption or transformations of electroactive and chemically reactive thin films. This is the first ever demonstration of combined neutron reflectivity and Love wave-based gravimetry and the experimental caveats, limitations and scope of the method are explored and discussed in detail
Structure within Thin Epoxy Films Revealed by Solvent Swelling: A Neutron Reflectivity Study
Solar heat reflective coating formed of polystyrene chains bearing 4-vinylpyridine-rich end segments
How does solvent annealing influence stress-driven surface undulations in polymer composite films with immobilized film-spanning nanoparticles?
Nucleated dewetting of thin polymer films
A combination of optical microscopy and neutron reflectometry is utilized to investigate the dewetting caused by a nucleation and growth process. The model system is polystyrene (PS) on top of Si (100) with its native oxide layer. Nucleation is forced by the introduction of additional grains during the sample preparation. From neutron scattering the density profile as an averaged piece of information is gained. Optical microscopy enables the in-situ determination of lateral local structures. The growth of the hole area of individual holes is described within the Kolmogorov model. The growth exponent as a function of annealing time of all holes investigated shows a linear increase
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