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For decades, superfluid helium has attracted the interest of the scientific community as an extremely pure realisation of a quantum liquid, only accessible at temperatures close to absolute zero. Previously, helium films have only been observed directly using X-rays. However, this method is limited to temperatures above 1 K due to the high levels of energy deposition, and it also suffers from an inability to distinguish between helium isotopes. Here we show that a 3He layer on top of a phase separated mixture film at 170 mK gradually dissolves into the 4He with increasing temperature. We also observe an anomaly in film behaviour near 300 mK and unexpected restoration of the layered structure at 1.5 K which is consistent with a re-entrant phase transition leading to the suppression of superfluidity in the film near 300 mK. Our successful application of neutron scattering to study helium films at ultra-low temperatures opens up new possibilities for future research. Superfluidity, a liquid exhibiting frictionless flow, is so far limited to observations in low-temperature 3He and 4He, where the underlying mechanisms governing the quantum state are complex and different for each isotope, making for a fascinating but challenging phenomenon to study experimentally. The authors use isotope-sensitive neutron reflectometry to investigate mixed 3He/4He superfluid He films on a Si surface, and resolve the structural features and phase transitions that occur with changing temperature. [ABSTRACT FROM AUTHOR]

As a result of the availability of modern software and hardware, Bayesian analysis is becoming more popular in neutron and X‐ray reflectometry analysis. The understandability and replicability of these analyses may be harmed by inconsistencies in how the probability distributions central to Bayesian methods are represented in the literature. Herein advice is provided on how to report the results of Bayesian analysis as applied to neutron and X‐ray reflectometry. This includes the clear reporting of initial starting conditions, the prior probabilities, the results of any analysis and the posterior probabilities that are the Bayesian equivalent of the error bar, to enable replicability and improve understanding. It is believed that this advice, grounded in the authors' experience working in the field, will enable greater analytical reproducibility in the work of the reflectometry community, and improve the quality and usability of results. [ABSTRACT FROM AUTHOR]

The experimental evidence of the exchange bias (EB) effect in epitaxial heterostructures of ferromagnetic La0.67Sr0.33MnO3 (LSMO) and paramagnetic LaNiO3 (LNO) grown on MgO(001) substrates is reported. The macroscopic magnetization measurements show a clear indication of EB in LNO/LSMO and LSMO/LNO/LSMO heterostructures. The strength of the exchange coupling rapidly reduces as the temperature is increased and almost vanishes above 50 K. Using spin dependent polarized neutron reflectometry (PNR) detailed depth dependent magnetization profiles of the heterostructures are investigated to understand the role of interface magnetism in the observed EB. PNR results establish the emergence of the interfacial ferromagnetic LNO layer of thickness ≈22–35 Å (≈6–9 unit cell) and magnetization ≈80 emu cc−1 at the LNO/LSMO interface for T < 100 K. The PNR results also show both ferromagnetic and anti‐ferromagnetic coupling between the LSMO and interfacial LNO layers, which may be dependent on the stacking order. The emergence of ferromagnetism in the interfacial paramagnetic LNO layer with unexpected EB in these heterostructures suggests a promising platform toward the effective realization of magnetic devices. [ABSTRACT FROM AUTHOR]

The article discusses study on interface-coupled bismuth ferrite, BiFeO3(BFO)/bismuth magnesium oxide, BiMnO3 (BMO) superlattices with magnetic transition temperature up to 410 Kelvin. Topics discussed include ferroelectricity in perovskite oxides, verification of epitaxy as well as the phase purity of the superlattices and magnetic transitions and clear magnetization at temperatures above the critical temperature of BMO.

Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism ( TC ∼ 600K), with a room temperature saturation moment ( MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. [ABSTRACT FROM AUTHOR]

We have used Soxhlet solvent purification to fractionate a broad molecular weight distribution of the polycarbazole polymer PCDTBT into three lower polydispersity molecular weight fractions. Organic photovoltaic devices were made using a blend of the fullerene acceptor PC71BM with the molecular weight fractions. An average power conversion efficiency of 5.89% (peak efficiency of 6.15%) was measured for PCDTBT blend devices with a number average molecular weight of Mn = 25.5 kDa. There was significant variation between the molecular weight fractions with low (Mn = 15.0 kDa) and high (Mn = 34.9 kDa) fractions producing devices with average efficiencies of 5.02% and 3.70% respectively. Neutron reflectivity measurements on these polymer:PC71BM blend layers showed that larger molecular weights leads to an increase in the polymer enrichment layer thickness at the anode interface, this improves efficiency up to a limiting point where the polymer solubility causes a reduction of the PCDTBT concentration in the active layer. [ABSTRACT FROM AUTHOR]

The performance characteristics of the Off Specular MicrOstrip Neutron Detector (OSMOND) are described. Based on microstrip gas chamber (MSGC) detectors, OSMOND is a high counting rate detector, with sub-millimeter position resolution, capable of replacing the existing rate limited scintillator detectors currently in use on the suite of reflectometer instruments of the ISIS spallation neutron source. The detector system is described together with results of neutron beam tests carried out on the CRISP and POLREF reflectometers. [ABSTRACT FROM PUBLISHER]

In this paper we investigate the domain wall pinning positions at parabolic pinning potentials in Gd doped Ni80Fe20 wires. Increasing the Gd doping percentage favors the formation of vortex domain walls, shown to be due to an increase in the out of plane anisotropy, allowing the pinning of a vortex and a transverse domain wall in two similar parabolic pinning potentials. Using pulsed currents to investigate the difference in the depinning characteristics of these two domain wall types, we show that the current density required for steady domain wall motion is smaller than the current density required to set it in motion and estimate this difference to be of the order 1011 A/m². [ABSTRACT FROM AUTHOR]