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31.
de Visser A Graf MJ Estrela P Amato A Baines C Andreica D Gygax FN Schenck A 《Physical review letters》2000,85(14):3005-3008
Transverse-field muon spin relaxation measurements have been carried out on the heavy-fermion superconductor UPt (3) doped with small amounts of Pd. We find that the critical Pd concentration for the emergence of the large-moment antiferromagnetic phase is approximately 0.6 at. %Pd. At the same Pd content, superconductivity is completely suppressed. The existence of a magnetic quantum critical point in the phase diagram, which coincides with the critical point for superconductivity, provides evidence for ferromagnetic spin-fluctuation mediated odd-parity superconductivity, which competes with antiferromagnetic order. 相似文献
32.
Bono D Mendels P Collin G Blanchard N Bert F Amato A Baines C Hillier AD 《Physical review letters》2004,93(18):187201
We present muSR experiments in the S=3/2 kagomé bilayer compound Ba(2)Sn(2)ZnGa(10-7p)Cr(7p)O22 [BSZCGO(p)] and compare it to the isostructural SrCr(9p)Ga(12-9p)O19 [SCGO(p)], including for the latter new results for p > or =0.89. Quantum-dynamical low energy magnetic excitations are evidenced in this novel compound. We study the evolution of the muon relaxation rate with p, T, and field. A phenomenological model for the muon relaxation based on sporadic dynamics due to spin excitations in a singlet sea proposed by Uemura et al. is extended to all fields and T range. Its connection to the RVB picture is discussed, and we argue that such coherent states might mediate the interactions between "impurities" which induce the spin glass freezing. 相似文献
33.
The mechanism of the addition of nonenolizable aldehydes and ketones to group 14 (di)metallenes has been examined through a theoretical study of the addition of formaldehyde to Si=C, Ge=C, Si=Si, Si=Ge, and Ge=Ge bonds at the B3LYP/6-311++G(d,p) and CAS-MCQDPT2/6-31++G(d,p) levels of theory. The reaction pathways located can be grouped as either involving the formation of singlet diradical or zwitterionic intermediates or as concerted processes. Within each group of reaction pathways, several different mechanisms have been located, with not all mechanisms being available to all of the (di)metallenes. It was found that for reactions in which a Si-O bond results (i.e., addition to Si=C, Si=Si, and Si=Ge) both diradical and zwitterionic intermediates are possible; however, the formation of diradical intermediates was not found for reactions that result in the formation of a Ge-O bond (addition to Ge=C and Ge=Ge). The underlying cause of this pathway selectivity is examined, as well as the effect of solvent on the relative energies of the pathways. The results of the study shed light on the cause of experimentally obtained results regarding the mechanism of the reaction of (di)metallenes with nonenolizable ketones and aldehydes. 相似文献
34.
F. Semadeni A. Amato B. Roessli P. Böni C. Baines T. Masuda K. Uchinokura G. Shirane 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):307-311
The temperature-concentration phase diagram of the Si-doped spin-Peierls compound CuGeO3 is investigated by means of neutron scattering and muon spin rotation spectroscopy in order to determine the microscopic
distribution of the magnetic and lattice dimerised regions as a function of doping. The analysis of the zero-field muon spectra
has confirmed the spatial inhomogeneity of the staggered magnetisation that characterises the antiferromagnetic superlattice
peaks observed with neutrons. In addition, the variation of the macroscopic order parameter with doping can be understood
by considering the evolution of the local magnetic moment as well as of the various regions contributing to the muon signal.
Received 6 September 2000 and Received in final form 29 January 2001 相似文献
35.
The Addition of Nitriles to Tetramesityldisilene: A Comparison of the Reactivity between Surface and Molecular Disilenes
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Dr. Julie A. Hardwick Prof. Kim M. Baines 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2480-2488
The addition of acetonitrile, propionitrile, and phenylacetonitrile to tetramesityldisilene (Mes2Si?SiMes2) was examined. In general, 1,2,3‐azadisiletines and the tautomeric enamines were formed, although a ketenimine was formed as the major product in the addition of phenylacetonitrile to the disilene. In the presence of LiCl, the mode of addition changed for both acetonitrile and propionitrile: insertion into the α‐CH bond of acetonitrile and/or formation of the formal HCN adduct was observed. Preliminary investigations of the reactivity of the nitrile adducts are also reported. A comparison between the reactivity of nitriles with Mes2Si?SiMes2 and the Si(100)‐2×1 surface was made both in terms of the types of adducts formed and their reactivity. Some insights into the surface chemistry are offered. 相似文献
36.
Addition of Isocyanides to Tetramesityldigermene: A Comparison of the Reactivity between Surface and Molecular Digermenes
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Nada Y. Tashkandi Emily E. Cook Jeremy L. Bourque Prof. Kim M. Baines 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):14006-14012
The reaction of benzyl isocyanide, tert‐butyl isocyanide, and 2,6‐dimethylphenyl isocyanide with tetramesityldigermene (Mes2Ge=GeMes2) was examined. Whereas the addition of benzyl isocyanide gave the C?NC activation product, Mes2Ge(CH2Ph)Ge(CN)Mes2, tert‐butyl isocyanide, and 2,6‐dimethylphenyl isocyanide did not give stable adducts, rather the rate of conversion of the digermene to the corresponding cyclotrigermane was accelerated. A comparison between the reactivity of the isocyanides with Mes2Ge=GeMes2 and the Ge(100)‐2×1 surface was made and some insights into the surface chemistry are offered. 相似文献
37.
Krasnoperov E. Meilikhov E. E. Baines C. Herlach D. Solt G. Zimmermann U. Eshchenko D. 《Hyperfine Interactions》1996,97(1):347-355
Muon spin relaxation in solid3He depends non-monotonously on the temperature. It is shown that this is entirely due to the magnetic dipole-dipole interactions. The observed line narrowing cannot be explained by the mechanism of positive charge hopping described by an Arrhenius-like law. The relaxation rate at low temperatures was found to increase under the influence of an external electric field. 相似文献
38.
M. J. Baines 《Numerical Methods for Partial Differential Equations》1994,10(2):191-203
It is shown that, for a class of time-dependent partial differential equations of the form ut = ??u, one step of the moving finite-element (MFE) procedure corresponds to one iteration of an algorithm for obtaining best L2 fits with adjustable nodes to continuous functions. In the steady-state limit the MFE procedure gives the best fit of ??u, with adjustable nodes, to the null function. For first-order partial differential equations, the MFE procedure moves nodes with approximate characteristic nodal speeds. We identify an additional speed component arising directly from the L2 projection which seeks a best fit in the sense described above. © 1994 John Wiley & Sons, Inc. 相似文献
39.
Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
40.
L. Schimmele A. Seeger W. Staiger W. Templ C. Baines A. Fritzsche M. Hampele D. Herlach K. Maier J. Major 《Hyperfine Interactions》1991,64(1-4):671-677
The longitudinalμ
+-spin relaxation rate has been measured on a high-purity spherical α-iron single crystal at temperaturesT down to 20 mK and in applied magnetic fieldsB
appl parallel to 〈111〉 up to 3 T. Only above 1 K can the data be satisfactorily described by one rate constantГ. At 1 T≤B
appl≤2 T and 50 mK≤T≤300 mK, oscillations (“wiggles”) were in addition superimposed on the longitudinal relaxation. A qualitative understanding
of the measurements may be achieved in terms of the increasing influence of internal stresses onμ
+ diffusion as the temperature is lowered. 相似文献