Ferromagnetism in Fe-doped Ba6Ge25 Chiral Clathrate

We have successfully synthesized a Ba6Ge25 clathrate, substituting 3 Fe per formula unit by Ge. This chiral clathrate has Ge sites forming a framework of closed cages and helical tunnel networks. Fe atoms randomly occupy these sites, and exhibit high-spin magnetic moments. A ferromagnetic transition is observed with Tc = 170 K, the highest observed Tc for a magnetic clathrate. However, the magnetic phase is significantly disordered, and exhibits a transformation to a re-entrant spin glass phase. This system has a number of features in common with other dilute magnetic semiconductors.Comment: Submitted to Applied Physics Letters. Fig. 1 resolution reduced for online archive versio

Electron spin resonance of Eu2+ in the Eu doped clathrate Ba6Ge25

We report electron spin resonance (ESR) investigations of the clathrate compound Ba6-xEuxGe25 (x=0.03-0.4) which exhibits a temperature induced, two-step reconstructive structure transformation at temperatures between 185 K and 223 K. The linewidth of the Eu2+ ESR proves to be sensitive to the transformation. Another anomaly in the temperature dependence of the linewidth is found near T=60 K which points towards another possible structural transition. Both anomalies seen in the ESR linewidth are not sensitive to the Eu content in contrast to the strong Eu-concentration dependence of transport properties. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005

(C6H14N2){Zn[ZnB2P4O15(OH)2]· (C6H13N2)Cl}_ A new templated zincoborophosphate

Colorless crystals of (C6H14N2){Zn[ZnB2P4O15(OH)(2)].(C6H13N2)Cl} (1) were prepared from mixtures of ZnCl2, B2O3, diaza-bicyclo[2.2.2] octane (DABCO), and 85% H3PO4 under mild hydrothermal conditions (170 degreesC). The crystal structure was determined by single-crystal X-ray diffraction (monoclinic, P2(1)/c (No. 14), a = 1704.3(1) pm, b = 937.03(5) pm, c = 1619.75(8) pro, beta = 96.894(3)degrees, Z = 2). The crystal structure contains tetrahedral zigzag ribbons, [ZnB2P4O15(OH)(2)](4-)}, running along [010]. Additional ZnO2NCl tetrahedra at the borders complete the ribbons by sharing common O-corners with the zincoborophosphate polymer. The nitrogen atoms of the quaternary ZnO2NCl tetrahedra belong to monoprotonated (HDABCO)(+) ions. A second (diprotonated) species, (H(2)DABCO)(2+), acts as a pure template and is fixed to adjacent zincoborophosphate ribbons along [100] via hydrogen bonds. The title compound 1 can be described as an adduct of (C6H14N2){Zn [ZnB2P4O15(OH)(2)]} with diaza-bicyclo[2.2.2]octane-hydrochloride. Thermoanalytical and X-ray powder diffraction investigations to high temperatures (740 degreesC) show the decomposition of 1 and the formation of a NH4[ZnBP2O8] polymorph as an intermediate

Nanoporous titanium borophosphates with rigid gainesite-type framework structure

China Scholarship Council (CSC); National Natural Science Foundation of China [40972035]Nanoporous titanium borophosphates have been synthesized which exhibit a rigid gainesite-type framework of polyhedra. The open-framework character is supported by the reversibility of de-and rehydration processes

High rate, fast timing Glass RPC for the high {\eta} CMS muon detectors

The HL-LHC phase is designed to increase by an order of magnitude the amount of data to be collected by the LHC experiments. To achieve this goal in a reasonable time scale the instantaneous luminosity would also increase by an order of magnitude up to $6.10^{34} cm^{-2} s^{-1}$ . The region of the forward muon spectrometer ($|{\eta}| > 1.6$) is not equipped with RPC stations. The increase of the expected particles rate up to $2 kHz/cm^{2}$ (including a safety factor 3) motivates the installation of RPC chambers to guarantee redundancy with the CSC chambers already present. The actual RPC technology of CMS cannot sustain the expected background level. The new technology that will be chosen should have a high rate capability and provides a good spatial and timing resolution. A new generation of Glass-RPC (GRPC) using low-resistivity (LR) glass is proposed to equip at least the two most far away of the four high ${\eta}$ muon stations of CMS. First the design of small size prototypes and studies of their performance in high-rate particles flux is presented. Then the proposed designs for large size chambers and their fast-timing electronic readout are examined and preliminary results are provided.Comment: 14 pages, 11 figures, Conference proceeding for the 2016 Resistive Plate Chambers and Related Detector

Search for the standard model Higgs boson decaying to a bbˉb\bar{b} pair in events with no charged leptons and large missing transverse energy using the full CDF data set

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at $\sqrt{s} = 1.96$ TeV recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45 fb$^{-1}$. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a $b$ quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and $150 \mathrm{GeV}/c^2$. For a Higgs boson mass of $125 \mathrm{GeV}/c^2$, the observed (expected) limit is 6.7 (3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV

A search for new physics is presented based on an event signature of at least three jets accompanied by large missing transverse momentum, using a data sample corresponding to an integrated luminosity of 36 inverse picobarns collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector at the LHC. No excess of events is observed above the expected standard model backgrounds, which are all estimated from the data. Exclusion limits are presented for the constrained minimal supersymmetric extension of the standard model. Cross section limits are also presented using simplified models with new particles decaying to an undetected particle and one or two jets

Search for the Higgs boson in events with missing transverse energy and b quark jets produced in proton-antiproton collisions at s**(1/2)=1.96 TeV

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use ~1 fb-1 integrated luminosity of proton-antiproton collisions at s**(1/2)=1.96 TeV recorded by the CDF II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248 +/- 43 (14.4 +/- 2.7) are expected from standard model background processes. We place 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 GeV/c2 to 140 GeV/c2. For a mass of 115 GeV/c2 the observed (expected) limit is 20.4 (14.2) times the standard model prediction.Comment: 8 pages, 2 figures, submitted to Phys. Rev. Let