Gail N. Iles

Anomalous magnetic field dependence of magnetocaloric effect at low temperature in Pr0.52Sr0.48MnO3 single crystal

We report the magnetocaloric effect (MCE) in a Pr0.52Sr0.48MnO3 single crystal. A peak in the temperature dependence of magnetic entropy change (ΔSM) with a fairly large negative value (≈3.8 J/kg K) is observed at 275 K close to Curie temperature. MCE is spread over a wide temperature range resulting in a considerable refrigerant capacity (≈293 J/kg). At low temperature the sign of ΔSM changes, below which anomalous field dependence of ΔSM is observed indicating the coexistence of ferromagnetic and antiferromagnetic interactions. Interplay between the interactions is strongly influenced by direction and magnitude of applied magnetic field in the ordered state.

Enhanced capability in a gas aggregation source for magnetic nanoparticles

We describe the characterization of a high-temperature (2000K) thermal gas aggregation source that is ultrahigh vacuum compatible and can cleanly deposit transition metal clusters with partial pressures of contaminants in the 10−11mbar range allowing codeposition with highly reactive matrices. In particular, we investigate the effect of varying (i) the bath gas pressure and composition on the size distribution and flux of clusters produced and (ii) the position of the crucible within the source. The mass spectra of Fe clusters produced, recorded using a quadrupole filter, show that changing the operating conditions and configuration of the source allow a wide range of cluster sizes—3000–320000amu (∼50–6000 atoms for Fe or Co) to be produced. We demonstrate the cleanliness of the source by producing uncontaminated Fe clusters in rare-earth matrices.

Magnetoelastic effect in MF2 (M = Mn, Fe, Ni) investigated by neutron powder diffraction

We have investigated the magnetoelastic effects in MF(2) (M = Mn, Fe, Ni) associated with the antiferromagnetic phase transition temperature T(N) by neutron powder diffraction. The temperature variation of the lattice parameters and the unit cell volume has been determined accurately with small temperature steps. From the temperature variation of the lattice parameters a, c and V the lattice strains Δa, Δc and ΔV associated with the antiferromagnetic phase transition have been extracted. Rietveld refinement of the crystal and magnetic structures from the diffraction data at low temperature gave a magnetic moment of 5.12 ± 0.09 μ(B), 4.05 ± 0.05 μ(B) and 1.99 ± 0.05 μ(B) per Mn, Fe and Ni ions, respectively. The lattice strains Δa, Δc and ΔV couple linearly with the intensity of the 100 magnetic reflection, which is proportional to square of the order parameter of the antiferromagnetic phase transition. The volume strains in MF(2) (M = Mn, Fe, Co, Ni) due to the magnetostriction vary smoothly along the transition metal series and seem to be correlated with the strength of the exchange interaction and the moments of the magnetic ions.

EMU: High-Resolution Backscattering Spectrometer at ANSTO

Volume 27 • Number 2 • 2016 Neutron News 20 Introduction EMU is a cold-neutron backscattering spectrometer installed (Fig. 1) in the neutron guide hall of the OPAL research reactor at ANSTO. It is a crystal analyser spectrometer based on Si (111) crystals confi gured in backscattering to achieve a high energy resolution [1]. It is thus very similar in function to several other operational backscattering spectrometers in the United States, Germany, France, and Japan [2–6]. Materials research facilitated by the EMU backscattering spectrometer is foreseen to include quasielastic neutron scattering studies of molecular dynamics in model biomolecules, functional polymers, hybrid nanocomposites and confi nement, as well as neutron spectroscopy studies of nuclear magnetism and quantum rotational tunnelling. EMU delivers a constant full-width half maximum resolution of ~1.1 μeV at the elastic line, for a total energy transfer range of ±28 μeV, across an elastic momentum transfer range spanning ~0.1 to 1.95 Å-1. Spectrometer design and features A key design consideration for EMU was to achieve a high energy resolution while maintaining an attractive count rate, deemed important to promote a neutron spectroscopy technique new to Australia. EMU was designed and built within the Bragg Institute Neutron Beam Expansion Program (NBI-2) [7], with a project budget allocated mid 2010 and a fi rst spectrum measured early 2015 (Fig. 2). Owing to unforeseen technical complications the spectrometer will commence user operation late 2016. Further to considerations of a time-of-fl ight [5] or phase-space-transforming chopper [2], a double-premomochromator [8] primary spectrometer design was fi nally opted for. Its merit is to allow in principle high signal-to-noise ratio and high resolution, for a relatively compact footprint. The spectrometer design principle and implementation (Fig. 3) closely follow those of the fi rst IN16 specEMU: high-resolution backscattering spectrometer at ANSTO

Hot carrier transfer processes in nonstoichiometric titanium hydride

The absorber of the hot carrier solar cell (HCSC) needs to have a considerably reduced hot carrier thermalisation rate, in order to maintain the photo-generated hot carriers for enough time such that they can be extracted. The slow carrier cooling effect is predicted in materials in which the phononic band gap is sufficiently large to block the Klemens decay. Binary compounds with a large mass ratio between the constituent elements are likely to have large phononic band gap. Titanium hydride is one of these binary compounds that has the potential to become an absorber of the HCSC. Whilst a large phononic gap has been observed in stoichiometric TiH2, it has not been experimentally confirmed for hydrogen deficient TiH x (where x < 2). In this article, we report the phonon density of states of TiH1.65 measured using inelastic neutron scattering and presented to clearly show the phononic band gap. We also present the carrier thermalisation process of a TiH x (1< x <2) thin film by transient absorption, and estimate the carrier cooling time in this material.

Direct evidence for the magnetic ordering of Nd ions in NdFeAsO by high-resolution inelastic neutron scattering

We investigated the low energy excitations in the parent compound NdFeAsO of the Fe-pnictide superconductor in the μeV range by a back scattering neutron spectrometer. The energy scans on a powder NdFeAsO sample revealed inelastic peaks at E = 1.600 ±0.003μeV at T = 0.055 K on both energy gain and energy loss sides. The inelastic peaks move gradually towards lower energy with increasing temperature and finally merge with the elastic peak at about 6 K. We interpret the inelastic peaks to be due to the transition between hyperfine-split nuclear level of the 143Nd and 145Nd isotopes with spin I=7/2. The hyperfine field is produced by the ordering of the electronic magnetic moment of Nd at low temperature and thus the present investigation gives direct evidence of the ordering of the Nd magnetic sublattice of NdFeAsO at low temperature.

The HZB neutron Laue diffractometer: From E11 to FALCON

Introduction In 2011 Professor Susan Schorr was awarded 300.000,00€ by the Helmholtz Association to build a neutron Laue diffractometer at the BER-II reactor in Berlin. Such an instrument had always been missing from the HZB instrument suite therefore, this became one of the fi rst projects within the newly formed department of crystallography. Dr. Gail N. Iles joined the department on a three-year post-doc contract as project manager and instrument responsible for the Laue project.

International Workshop on Neutron Laue Diffraction

Neutron News Volume 24 • Number 3 • 2013 3 S Max von Laue produced the fi rst diffraction pattern 100 years ago in Munich, we have seen huge advances in instrumentation from laboratory X-ray sources to largeuser facilities offering radiation over a wide range of wavelengths from both synchrotron X-rays and neutrons. The Laue technique offers the unique opportunity to generate an image of a large volume of reciprocal space in a single image. Samples from as diverse a range of fi elds as protein crystallography to geoscience can be investigated and an equally wide range of sample environments can be accommodated. In recent years newer instruments have replaced neutron image plates with CCD technology enabling splitsecond measurements of samples. We are also at the dawn of combined high-pressure/high-temperature studies of single crystals using neutron Laue diffraction. On 11 December 2012, the Helmholtz-Zentrum Berlin (HZB) held a workshop to present a summary of neutron Laue instruments around the world, to explore methods of data analysis for large amounts of data and to begin an investigation of user requirements for extreme sample environments. The Workshop was opened by Susan Schorr, HZB. Gail N. Iles, HZB, presented the current status of the new Laue diffractometer at HZB called ‘FALCON’ – Fast Acquisition Laue Camera fOr Neutrons. Via live linkup from Sydney, Alison Edwards and Ross Piltz from ANSTO presented some fascinating results from the image plate Laue diffractometer, KOALA. The latest developments of the Laue instruments LADI and VIVALDI at ILL were shown by Marie-Hélène Lemée-Cailleau presenting a comparison of the samples that can be measured using cold and thermal neutrons, respectively. Bachir Ouladdiaf, ILL, presented the latest images generated by CYCLOPS; a double octagonal array of CCD (Charged Coupled Device) neutron cameras, demonstrating that it is possible to perform a full structure determination in two hours. Silvia Capelli, ILL, went on to explain the technique of backscattering for the rapid orientation of crystals using Orient Express. Orient Express at ILL has measured over 1000 samples and been used in over 500 experiments. Matthias Gutmann, ISIS, presented the UK Laue instrument SXD and the software he has developed over the past ten years for analysis of such Laue data. John Helliwell, University of Manchester, presented LAUEGEN on which most Laue data analysis programs are based on. John spoke about the challenges we now face when dealing with the huge amounts of data that Laue machines using CCD technology create. Using a dataset from the Laue instrument at Oak Ridge National Laboratory, Tim Grüne, Göttingen University, showed step by step refi nement of a Rubredoxin sample using Shelxl-2012 software. John Loveday, University of Edinburgh, highlighted the importance of calibrating your detector when using the Paris-Edinburgh cell and controlling the background scatterers. At the end of the workshop a lively discussion ensued whereby Werner Schweika, European Spallation Source, asked for input for a potential Laue Diffractometer to be included in the instrument suite of the ESS. Prestigious participants were not restricted to the list of invited speakers, Alan Hewat, member of the HZB advisory committee, made many valuable contributions throughout the day. The International Workshop on neutron Laue diffraction provided the perfect opportunity for the world-leaders in the fi eld to meet and discuss instrumentation, software and scientifi c options for the future. One thing is certain, neutron Laue diffraction is as exciting and challenging today as the discovery by its namesake 100 years ago.

Agglomeration of Ni-nanoparticles in the gas phase under gravity and microgravity conditions

The agglomeration of metallic nanoparticles can be performed using the well-known inert gas condensation process. Unfortunately, thermal effects such as convection are created by the heating source and as a result the turbulent aerosol avoids ideal conditions. In addition, the sedimentation of large particles and/or agglomerates influences the self-assembly of particles. These negative effects can be eliminated by using microgravity conditions. Here we present the results of the agglomeration of nanoscale Ni-particles under gravity and microgravity conditions, the latter provided by adapted microgravity platforms namely the European sounding rocket MAXUS 8 and the European Parabolic Flight aircraft, Airbus A300 Zero-G.

Nanoparticle Agglomeration Payloads For Microgravity Experimentation

Two microgravity compatible experiments for inert gas evaporation/condensation of metals have been developed both for manual operation on-board parabolic flights and for automatic operation on-board a MAXUS sounding rocket. Two different evaporation methods have been utilised in each experiment i.e., induction coil heating in the aeroplane setup and resistive wire heating for the sounding rocket equipment. In this paper we present the challenges and technical solutions in down-scaling a complex and manually operated experiment developed for parabolic flight campaigns to the size, weight, and power constraints of a sounding rocket payload.