142 research outputs found
Petrogenesis and geochemical halos of the amphibolite facies, Lower Proterozoic, Kerry Road volcanogenic massive sulfide deposit, Loch Maree Group, Gairloch, NW Scotland
The Palaeoproterozoic Kerry Road deposit is one of the oldest examples of volcanogenic massive sulfide (VMS) mineralization. This small VMS deposit (~500,000 tons grading at 1.2% Cu, 3.5% Zn) is hosted in amphibolite facies mafic-siliciclastic units of the c. 2.0 Ga Loch Maree Group, Scotland. Sulfide mineralization consists of pyrite and pyrrhotite with subordinate chalcopyrite and sphalerite, occurring in disseminated, vein and semi-massive to massive textures. The deposit was highly deformed and metamorphosed during the c. 1.8–1.7 Ga Laxfordian Orogeny. Textural relationships of deformed sulfide minerals, related to early Laxfordian deformation (D1/D2), indicate initial high pressure-low temperature (100 MPa, 150 °C) conditions before reaching peak amphibolite facies metamorphism, as evident from pyrrhotite crossing the brittle/ductile transition prior to chalcopyrite. Late Laxfordian deformation (D3/D4) is marked by local retrograde greenschist facies at low pressure and temperature (<1.2 MPa, <200 °C), recorded by late red sphalerite remobilization. δ34S values from all sulfide minerals have a homogeneous mean of 0.8 ± 0.7‰ (n = 21), consistent with interaction of hydrothermal fluids in the host oceanic basalt-island arc setting envisaged for deposition of the Loch Maree Group. Microprobe analyses of amphiboles record evidence of the original alteration halo associated with the Kerry Road deposit, with a systematic Mg- and Si- enrichment from ferrotschermakite (~150 m) to Mg-hornblende (~90 m) to actinolite (0 m) on approach to the VMS deposit. Furthermore, whole rock geochemistry records a progressive enrichment in Si, Cu, Co, and S, and depletion in Al, Ti, V, Cr, Y and Zr with proximity to the VMS system. These elemental trends, together with amphibole geochemistry, are potentially useful exploration vectors to VMS mineralization in the Loch Maree Group, and in similar highly deformed and metamorphosed terranes elsewhere.PostprintPeer reviewe
The effect of deuteration on organic magnetoresistance
NOTICE: this is the author’s version of a work that was accepted for publication in Synthetic Metals. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in SYNTHETIC METALS, 161, 7-8, (2011) DOI 10.1016/j.synthmet.2010.11.04
Temperature Dependence of Low-Lying Electronic Excitations of LaMnO_3
We report on the optical properties of undoped single crystal LaMnO_3, the
parent compound of the colossal magneto-resistive manganites. Near-Normal
incidence reflectance measurements are reported in the frequency range of
20-50,000 cm-1 and in the temperature range 10-300 K. The optical conductivity,
s_1(w), is derived by performing a Kramers-Kronig analysis of the reflectance
data. The far-infrared spectrum of s_1(w) displays the infrared active optical
phonons. We observe a shift of several of the phonon to high frequencies as the
temperature is lowered through the Neel temperature of the sample (T_N = 137
K). The high-frequency s_1(w) is characterized by the onset of absorption near
1.5 eV. This energy has been identified as the threshold for optical
transitions across the Jahn-Teller split e_g levels. The spectral weight of
this feature increases in the low-temperature state. This implies a transfer of
spectral weight from the UV to the visible associated with the paramagnetic to
antiferromagnetic state. We discuss the results in terms of the double exchange
processes that affect the optical processes in this magnetic material.Comment: 7 pages, 5 figure
Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939
We have searched and reviewed all multi- wavelength data available for the
region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain
its possible counterpart at lower energies. As a result, only a point-like
optical/infrared source with flat-spectrum radio emission is found to be
consistent with all X-ray and gamma-ray error circles. Its struc- ture is
marginally resolved at radio wavelengths at the sub-arcsecond level. An
extragalactic scenario appears to be the most likely interpretation for this
object.Comment: 5 pages, 3 figures, 1 tabl
Muonium avoided level crossing measurement of electron spin relaxation rate in a series of substituted anthradithiophene based molecules
Muon spin spectroscopy and in particular the avoided level crossing technique is introduced, with the aim of showing it as a very sensitive local probe for electron spin relaxation in organic semiconductors. Avoided level crossing data on tert-butyl-ethynyl anthradithiophene, tri-methyl-silyl-ethynyl anthradithiophene and tri-ethygermyl-ethynyl anthradithiophene at different temperatures are presented. This series of molecules have an identical anthradithiophene backbone, but we have performed a targeted substitution on the central atom of the two side groups, of C, Si and Ge. We extracted the electron spin relaxation for the three molecules of this series and discuss them in the context of previously published results
The UKIDSS Galactic Plane Survey
'The definitive version is available at www.blackwell-synergy.com .' Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.13924.xThe UKIDSS Galactic Plane Survey (GPS) is one of the five near-infrared Public Legacy Surveys that are being undertaken by the UKIDSS consortium, using the Wide Field Camera on the United Kingdom Infrared TelescopePeer reviewe
Magneto-transport and magnetic susceptibility of SmFeAsO1-xFx (x = 0.0 and 0.20)
Bulk polycrystalline samples, SmFeAsO and the iso-structural superconducting
SmFeAsO0.80F0.20 are explored through resistivity with temperature under
magnetic field {\rho}(T, H), AC and DC magnetization (M-T), and Specific heat
(Cp) measurements. The Resistivity measurement shows superconductivity for x =
0.20 sample with Tc(onset) ~ 51.7K. The upper critical field, [Hc2(0)] is
estimated ~3770kOe by Ginzburg-Landau (GL) theory. Broadening of
superconducting transition in magneto transport is studied through thermally
activated flux flow in applied field up to 130 kOe. The flux flow activation
energy (U/kB) is estimated ~1215K for 1kOe field. Magnetic measurements
exhibited bulk superconductivity with lower critical field (Hc1) of ~1.2kOe at
2K. In normal state, the paramagnetic nature of compound confirms no trace of
magnetic impurity which orders ferromagnetically. AC susceptibility
measurements have been carried out for SmFeAsO0.80F0.20 sample at various
amplitude and frequencies of applied AC drive field. The inter-granular
critical current density (Jc) is estimated. Specific heat [Cp(T)] measurement
showed an anomaly at around 140K due to the SDW ordering of Fe, followed by
another peak at 5K corresponding to the antiferromagnetic (AFM) ordering of
Sm+3 ions in SmFeAsO compound. Interestingly the change in entropy (marked by
the Cp transition height) at 5K for Sm+3 AFM ordering is heavily reduced in
case of superconducting SmFeAsO0.80F0.20 sample.Comment: 18 pages text + Figs: comments/suggestions welcome
([email protected]
Nernst effect of iron pnictide and cuprate superconductors: signatures of spin density wave and stripe order
The Nernst effect has recently proven a sensitive probe for detecting unusual
normal state properties of unconventional superconductors. In particular, it
may sensitively detect Fermi surface reconstructions which are connected to a
charge or spin density wave (SDW) ordered state, and even fluctuating forms of
such a state. Here we summarize recent results for the Nernst effect of the
iron pnictide superconductor , whose ground state evolves
upon doping from an itinerant SDW to a superconducting state, and the cuprate
superconductor which exhibits static stripe
order as a ground state competing with the superconductivity. In , the SDW order leads to a huge Nernst response, which allows
to detect even fluctuating SDW precursors at superconducting doping levels
where long range SDW order is suppressed. This is in contrast to the impact of
stripe order on the normal state Nernst effect in . Here, though signatures of the stripe order are
detectable in the temperature dependence of the Nernst coefficient, its overall
temperature dependence is very similar to that of ,
where stripe order is absent. The anomalies which are induced by the stripe
order are very subtle and the enhancement of the Nernst response due to static
stripe order in as compared to that of the
pseudogap phase in , if any, is very small.Comment: To appear in: 'Properties and applications of thermoelectric
materials - II', V. Zlatic and A. Hewson, editors, Proceedings of NATO
Advanced Research Workshop, Hvar, Croatia, September 19 -25, 2011, NATO
Science for Peace and Security Series B: Physics and Biophysics, (Springer
Science+Business Media B.V. 2012
Measurement of hyperfine coupling constants of muoniated radicals in small molecule semiconductors
We report the hyperfine coupling constants of muoniated radicals formed in a number of organic semiconductors, via transverse field measurements taken in the Paschen Back limit, and compare the results to avoided level crossing resonances. Five muoniated radicals are found in tetracene, despite there only being three potential non-equivalent bonding sites, and we suggest that this might be down to crystal packing effects. For 6,13-bis(triisopropylsilylethynyl) pentacene and 6,13-bis(trimethlsilylethynyl)-pentacene, we demonstrate that the transverse field data supports the previously published avoided level crossing resonances
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