Anton P. J. Stampfl

Does local disorder occur in the pyrochlore zirconates

The zirconates Ln(2)Zr(2)O(7) (Ln = lanthanoid) have been studied using a combination of Zr L-edge X-ray absorption near edge structure (XANES) and synchrotron X-ray and neutron powder diffraction methods. These studies demonstrate that as the size of the lanthanoid cation decreases, the local structure evolves smoothly from the ideal pyrochlore toward the defect fluorite rather than undergoing an abrupt transformation. The Zr L-edge spectrum is found to be extremely sensitive to changes in the local coordination environment and demonstrates an increase in local disorder across the pyrochlore oxides. The sensitivity of the XANES measurements enables us to identify the progressive nature of the transition that could not be detected using bulk diffraction techniques.

Surface electronic properties of ZnO nanoparticles

The surface electronic structure of ZnO nanoparticles has been studied with photoemission and x-ray absorption spectroscopies. Contrary to expectation, ZnO:Zn phosphor nanoparticles were found to contain a lower oxygen vacancy density on the surface than undoped ZnO counterparts, but oxygen vacancies are in different chemical environments. Cathodoluminescence shows intense green luminescence from the ZnO:Zn surface, while the undoped nanoparticles exhibit only the near-band-edge emission. The results indicate the roles of surface oxygen vacancies and their environment in the previously unexplained green luminescence from the ZnO:Zn material.

The magnetic structure of an epitaxial BiMn0.5Fe0.5O3 thin film on SrTiO3 (001) studied with neutron diffraction

High-angle neutron diffraction was used to directly reveal the atomic-scale magnetic structure of a single-crystalline BiMn0.5Fe0.5O3 thin film deposited on a SrTiO3 (001) substrate. The BiMn0.5Fe0.5O3 phase exhibits distinctive magnetic properties that differentiate it from both parent compounds: BiFeO3 and BiMnO3. A transition to long-range G-type antiferromagnetism was observed below 120 K with a (121212) propagation vector. A weak ferromagnetic behavior was measured at low temperature by superconducting quantum interference device (SQUID) magnetometry. There is no indication of the spin cycloid, known for BiFeO3, in the BiMn0.5Fe0.5O3 thin film. The neutron diffraction suggests a random distribution of Mn and Fe over perovskite B sites.

Central‐Atom Size Effects on the Methyl Torsions of Group XIV Tetratolyls

The Group XIV tetratolyl series X(C(6)H(4)-CH(3))(4) (X = C, Si, Ge, Sn, Pb) were studied by using inelastic neutron scattering to measure the low-energy phonon spectra to directly access the methyl-group torsional modes. The effect of increased molecular radius as a function of the size of the central atom was shown to have direct influence on the methyl dynamics, reinforced with the findings of molecular dynamics and contact surface calculations, based upon the solid-state structures. The torsional modes in the lightest analogue were found to be predominantly intramolecular: the Si and Ge analogues have a high degree of intermolecular methyl-methyl group interactions, whilst the heaviest analogues (Sn and Pb) showed pronounced intermolecular methyl interactions with the whole phonon bath of the lattice modes.

The beryllium-filter spectrometer option on TAIPAN

Neutron News Volume 27 • Number 2 • 2016 27 Introduction A high-throughput low-energy band-pass fi lter spectrometer is a recent addition to the thermal triple-axis spectrometer, TAIPAN [1] at ANSTO. The so-called Befi lter spectrometer option is a near-faithful copy of the fi lter-spectrometer, FANS, located at the NIST Center for Neutron Research [2, 3]. Thus on TAIPAN one has the option of using either the triple axis-spectrometer or the newly built and commissioned Be-fi lter spectrometer. The triple-axis spectrometer’s focus is on the study of phonon modes and low-energy magnetic phenomena from single-crystal material whilst the Be-fi lter spectrometer measures the vibrational density of states from mainly powder samples that allows for a wide range of studies to be carried out in the fi elds of physics, chemistry, materials science, biology and so forth.

What Difference Does a Methyl Group Make: Pentamethylbenzene?

The crystal structure of pentamethylbenzene has been obtained for the first time with the use of synchrotron radiation, whilst the low-energy spectrum of lattice dynamics, dominated by the methyl group torsions, was obtained using inelastic neutron scattering. The effect of symmetry lowering by the removal of a single methyl group relative to hexamethylbenzene has been investigated, including the role that this plays in the charge-transfer characteristics of complexes formed with tetracyanoethylene.

Investigation of field-induced ferromagnetism in Pd–Ni–Fe–P metallic glass by x-ray magnetic circular dichroism

We have applied x-ray magnetic circular dichroism to investigate the field-induced ferromagnetism in Pd40Ni22.5Fe17.5P20 alloy. The experiment revealed that both Ni and Fe were in a divalent state and that the magnetic properties of the material were determined by the localized 3d electrons of the transition metals. No clear evidence of Ruderman–Kittel–Kasuya–Yosida-type interaction among magnetic clusters was observed. It is believed that the detailed balance of fundamental spin-orbit and exchange interactions as a function of temperature and applied magnetic field determine the different magnetic properties of the alloy.

The complementarity of PIXE and synchrotron induced X-ray methods for the characterisation of combustion sources contributing to urban air pollution

Abstract Current knowledge of fine-particle airborne pollution concentrations and constituents with diameters below 2.5 μm (PM2.5) is limited. Sources are both natural and man-made. Here we describe two types of experiments performed using the advanced photon source facility at Chicago, and compare the results with PIXE analysis on the same fine particle filters. These are firstly broad beam (2 mm) studies with tuned synchrotron beam energies to help resolve over-lapping X-rays, and secondly highly focused X-ray beam studies (0.2 μm) of individual fine particles from airborne pollution combustion sources.

Method for the measurement of anisotropy and rotational hysteresis using linear dichroism

A technique combining x-ray magnetic linear dichroism absorption spectroscopy and rotational hysteresis loops is demonstrated. This technique, x-ray magnetic linear loops (XMLL), is used to extract magnetocrystalline anisotropy information. Results from two systems, a polycrystalline Fe film, and an epitaxial Fe film which exhibit different magnetic anisotropies, are shown. The measured XMLL is described using a simple single-domain anisotropy model.