Opening the terahertz window on the OSIRIS spectrometer

4 pags., 6 figs. -- QENS/WINS 2014 - 11th International Conference on Quasielastic Neutron Scattering and 6th International Workshop on Inelastic Neutron SpectrometersA cooled and mechanically retractable beryllium filter has been installed and commissioned on the low-energy OSIRIS spectrometer at ISIS. This instrument development extends the energy-transfer range of the spectrometer up to ca. 20 meV (∼ 5 THz), leading to an excellent resolution at THz frequencies and substantial gains in detected flux relative to existing capabilities on the neighbouring IRIS spectrometer. Herein, we provide a concise account of this new capability for high-resolution neutron spectroscopy in the THz domain, as well as outline a number of ongoing and potential scientific opportunities in condensed-matter physics, chemistry, and materials science.The authors gratefully acknowledge the UK Science & Technology Facilities Council for financial support and access to beam time at ISIS

Anomalous magnetic exchange in a dimerized quantum magnet composed of unlike spin species

We present here a study of the magnetic properties of the antiferromagnetic dimer material CuVOF 4 ( H 2 O ) 6 ⋅ H 2 O , in which the dimer unit is composed of two different S = 1 / 2 species, Cu(II) and V(IV). An applied magnetic field of μ 0 H c 1 = 13.1 ( 1 ) T is found to close the singlet-triplet energy gap, the magnitude of which is governed by the antiferromagnetic intradimer J 0 ≈ 21 K, and interdimer J ′ ≈ 1 K, exchange energies, determined from magnetometry and electron-spin resonance measurements. The results of density functional theory (DFT) calculations are consistent with the experimental results. The DFT calculations predict antiferromagnetic coupling along all nearest-neighbor bonds, with the magnetic ground state comprising spins of different species aligning antiparallel to one another, while spins of the same species are aligned parallel. The magnetism in this system cannot be accurately described by the overlap between localized V orbitals and magnetic Cu orbitals lying in the Jahn-Teller (JT) plane, with a tight-binding model based on such a set of orbitals incorrectly predicting that interdimer exchange should be dominant. DFT calculations indicate significant spin density on the bridging oxide, suggesting instead an unusual mechanism in which intradimer exchange is mediated through the O atom on the Cu(II) JT axis

Pressure Dependent Magnetism in Y1.05(Mn0.95Al0.05)2

The Laves phase compound YMn2 exhibits a discontinuous transition from a spin fluctuating Pauli paramagnetic state above 110 K to an expanded, localised moment helical antiferromagnetic state below 110 K. Substitution of Al for Mn in the pseudo-binary compound Y(Mn1-xAlx)2 exerts a negative chemical pressure, expanding the unit cell and further localizing the Mn moment. Here we present the results of a μSR study of spin fluctuations in Y(Mn1-xAlx)2 (x = 0.05) in which external mechanical pressure (4.5 kbar) is applied to counteract the Al induced chemical pressure and destabilize the local Mn moment

Development and characterization of a new bio nanocomposite bio NCP for diagnosis and treatment of breast cancer

Breast cancer is a public health problem throughout the world. Moreover, breast cancer cells have a great affinity for hydroxyapatite, leading to a high occurrence of bone metastasis. In this work we developed a bio nanocomposite bio NCP in order to use such affinity in the diagnosis and treatment of breast cancer. The bio NCP consists of magnetic nanoparticles of Mn and Zn ferrite inside a polymeric coating chitosan modified with nanocrystals of apatite. The materials were characterized with synchrotron X ray Powder Diffraction XPD , Time of Flight Neutron Powder Diffraction NPD , Fourier Transformed Infra red Spectroscopy FTIR , Scanning Electron Microscopy SEM and magnetic measurement with a Physical Property Measurement System PPMS . We obtained ferrite nanoparticles with a high inversion degree of the spinel structure regarding the Fe and Mn, but with all the Zn in the A site. The coating of such nanoparticles with chitosan had no notable effects to the ferrite microstructure. In addition, the polymeric surface can be easily modified with apatite nanocrystals since the hydration of the bio NCP during synthesis can be controlled. The resulting bio NCP presents a spherical shape with a narrow size distribution and high magnetic response at room temperature and is a very promising material for early diagnosis of breast cancer and its treatmen

Benzene diffusion on graphite described by a rough hard disk model

9 pags.; 5 figs.; 1 tab.; 2 apps.© 2014 Elsevier Ltd. All rights reserved. New insight into the nature of diffusion and the origin of friction of a prototype system for weak physisorption-benzene molecules, C6H6, adsorbed on the basal plane (0001) of graphite-has been obtained with quasi-elastic neutron scattering (QENS). Spectra were measured at relative adsorbate coverages between 0.1 and 1.0 monolayers (ML) and at sample temperatures between 60 K and 140 K. Our experimental observations require a substantial modification of the model of interaction between benzene molecules and graphite surfaces: in contrast to recent studies we find only weak kinetic surface friction, but a substantial dissipative interaction during inter-molecular collisions. At coverages of up to 0.5 ML the molecular dynamics are successfully modeled by a rough hard disk model, which we derive from a three-dimensional rough hard sphere model. At the full monolayer, three body and higher order collisions are dominant and the rough hard disk model breaks down, as expected.Peer Reviewe

Analysis of the crystallographic and magnetic structures of the Tb0.1Pr0.9Al2 and Tb0.25Pr0.75Al2 magnetocaloric compounds by means of neutron scattering

Neutron powder diffraction and inelastic neutron scattering data were used to simulate and understand the magnetization and heat capacity curves of the pseudobinary Tbx Pr1 amp; 8722;x Al2, with x 0.10 and 0.25, as a function of temperature. From the Rietveld analysis, we concluded that no crystallographic transition occurs in these samples, and the high symmetry of the magnetic structure was confirmed. Moreover, the different contributions from the reflection planes could be related to the known exchange bias like effect characteristic for the x 0.25 sample, also suggesting the existence of some rearrangement of the magnetic moments or even the presence of spin frustration in this system. Finally, the obtained set of theoretical parameters using the mean field approach for the two systems consisting of two sublattices allowed the experimental data to be described and to explain their physical behaviors. The ensemble of our results leads us to affirm that the quadrupolar interactions as well as an existence of some rearrangement of the magnetic moments or a frustration play an important role in the strong unidirectional anisotropy and the exchange bias like effect observed in this pseudobinary syste

Human hair: subtle change in the thioester groups dynamics observed by combining neutron scattering, X-ray diffraction and thermal analysis

Hair analysis plays an important role in forensic toxicology and biomonitoring tests. However, cosmetic treatments cause changes to the hair. Thus, a better understanding of the hair’s structure and the factors that influence its composition is critical. It is known that oxidative treatments modify the hair chemical, structural and mechanical properties. These treatments also cause degradation of the melanin as well as of the structures present in the hair cuticle and cortex. Considering that the literature is unanimous regarding the increase in hydrophilicity and porosity promoted in human hair by bleaching, in this work we investigated how this oxidative damage is triggered. By combining several techniques, inelastic and quasi-elastic neutron scattering, differential scanning calorimetry, thermal gravimetric analysis and X-ray diffraction, we were able to connect the chemical and structural changes to a subtle dynamic modification of the proton mobility in the hair fibers. In addition, alterations in the thermal behavior evidenced a small denaturation of α-keratin intermediate filaments and a slight decrease in the amount of confined water in the hair fibers. Moreover, data obtained by neutron spectroscopy indicated that bleaching attacks the thioester groups of the proteins causing larger proton mobility of the hydrogenous components (water, protein and/or lipids)

Neutron diffraction in situ monitoring of the dislocation density during martensitic transformation in a stainless steel

International audienceIn situ monitoring of the dislocation density during martensitic transformation, and annealing, of the martensitic stainless steel 17-4PH was undertaken using neutron diffraction. The dislocation density in martensite is seen to increase linearly from ∼2 × 1015 to ∼4 × 1015 m−2 during the transformation. In addition, the dislocation density in the parent phase (austenite) slowly increases from ∼0 to 1015 m−2. Annealing of the newly formed martensite in the temperature range 500-700 °C leads to almost complete elimination of dislocations