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71.
A. V. Lukoyanov V. V. Mazurenko V. I. Anisimov M. Sigrist T. M. Rice 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(2):205-207
We propose FeSb2 to be a nearly ferromagnetic small gap semiconductor, hence a direct analog
of FeSi. We find that despite different compositions and crystal structures,
in the local density approximation with on-site Coulomb repulsion correction (LDA+U) method
magnetic and semiconducting solutions for U=2.6 eV are energetically degenerate
similar to the case of FeSi. For both FeSb2 and FeSi (FeSi1-xGex alloys)
the underlying transition mechanism allows one to switch from a small gap semiconductor
to a ferromagnetic metal with magnetic moment ≈1 μB per Fe ion with external magnetic field. 相似文献
72.
The oxidation of benzo[a]azulene ( 4 ) with commercial MnO2 in dioxane/H2O leads to a number of products in low yield (Table 1). Treatment of 4 with ‘mild’ MnO2 (MnO2/C) in dioxane/5% H2O results in the formation of 10,10′‐bibenzo[a]azulene ( 18 ) in yields of up to 59% of isolated and purified material. Compound 18 exhibits atropisomerism and can be separated by HPLC on a Chiralcel column at room temperature into its stable antipodes (Fig.). 相似文献
73.
Kasper S. Pedersen Marc Sigrist Mikkel A. Sørensen Dr. Anne‐Laure Barra Dr. Thomas Weyhermüller Dr. Stergios Piligkos Dr. Christian Aa. Thuesen Morten G. Vinum Hannu Mutka Dr. Høgni Weihe Dr. Rodolphe Clérac Prof. Dr. Jesper Bendix 《Angewandte Chemie (International ed. in English)》2014,53(5):1351-1354
A facile synthesis of the [ReF6]2? ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF6]2? unit in (PPh4)2[ReF6]?2 H2O ( 1 ) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one‐dimensional coordination polymer [Zn(viz)4(ReF6)]∞ ( 2 , viz=1‐vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy‐plane‐type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4(ReF6)]∞ ( 3 ) analogue in which the ferromagnetic NiII–ReIV interaction (+10.8 cm?1) dwarfs the coupling present in related cyanide‐bridged systems. These results reveal [ReF6]2? to be an unique new module for the design of molecule‐based magnetic materials. 相似文献
74.
Ying-Fen Ran Martin Steinmann Marc Sigrist Shi-Xia Liu Jürg Hauser Silvio Decurtins 《Comptes Rendus Chimie》2012,15(10):838-844
The explorative lanthanide coordination chemistry of 4′,5′-bis-(propylthio)tetrathiafulvenyl[i]dipyrido[3,2-a:2′,3′-c]phenazine (TTF-dppz) is described. Thereby, four new Ln(III) complexes, [Ln(NO3)3(TTF-dppz)2] with Ln(III) = Nd (1), Eu (2), Gd (3), Tb (4), have been prepared and characterized. An X-ray crystallographic study of [Gd(NO3)3(TTF-dppz)2] (3) shows that the Gd(III) ion is coordinated to six oxygen atoms from three bidentate nitrate ligands and four nitrogen atoms from two bidentate TTF-dppz molecules forming a distorted bicapped square antiprism coordination geometry. The UV-vis spectra of the four Ln(III) complexes show very strong absorption bands in the UV region consistent with ligand centred electronic π-π* transitions and an intense broad absorption band in the visible region corresponding to a spin-allowed electronic π-π* 1ILCT transition from the TTF-dppz ligand. Upon coordination, the 1ILCT band of the free TTF-dppz ligand is bathochromically shifted. The electrochemical studies reveal that all complexes undergo two reversible oxidation and one (quasi)reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the dppz unit, respectively. Moreover, the magnetic properties of complexes 3 and 4 are discussed. 相似文献
75.
76.
J. Pola Z. Bastl J. Tlskal H. Beckers H. BÜRger P. Moritz P. Weiss M. Sigrist 《应用有机金属化学》1993,7(6):381-389
Solid Si/C/H/F materials laser-deposited from gaseous fluoro-methylsilanes are examined by XPS, SEM, IR and Raman spectroscopy and revealed to be a blend of silicon-carbon-based frameworks, possessing some Si-H and C-H bonds, and carbon whose modification is dependent on the structure of the parent fluoromethylsilane. Their properties are affected by contact with the atmosphere: although incorporation of oxygen into silicon-carbon frameworks is a very fast process, the dramatically improved adhesion to aluminium requires long exposure periods. 相似文献
77.
We report on the extension of the emission wavelength range of a nanosecond pulsed commercial optical parametric oscillator (OPO) towards the infrared. By difference frequency mixing the idler of the OPO with the fundamental of its Nd:YAG pump laser the wavelength range from 2.5–4.5 μm is covered at considerable pulse energies. This laser source is then applied for the first time to photoacoustic trace gas spectroscopy in the fundamental C---H stretch band located around 3.3 μm. Spectra of single- and multi-component gas mixtures of volatile organic compounds are recorded and analyzed with respect to composition and concentration. The detection limits for the individual substances within the gas mixtures are found in the lower parts per million (ppm) range. 相似文献
78.
We describe and example the Beam Propagation Method (BPM) used to model and simulate nonlinear refractive and absorptive effects in materials with applications to optical limiting and switching. Various scenarios including laser-beam trapping and laser-beam division are investigated, in order to demonstrate the power of the BPM. A novel technique is also described for efficiently modelling the external far-field propagation from nonlinear media, including the propagation of non-Gaussian-shaped spatial profiles. The methods are finally combined with the phenomenon of nonlinear absorption to demonstrate enhanced power limiting in the presence of self-refraction. Optimal parameters for high-fluence power-limiting are subsequently discussed. 相似文献
79.
Density functional theory (DFT) and the valence bond configuration interaction (VBCI) model have been applied to the oximato-based Mn(III)(3)O single-molecule magnets (SMMs), allowing one to correlate the Mn(III)-Mn(III) exchange coupling energy (J) with the bridging geometry in terms of two structural angles: the Mn-O-N-Mn torsion angle (γ) and the Mn(3) out-of-plane shift of O (angle δθ). Using DFT, a two-dimensional (γ, δθ) energy surface of J is derived and shown to yield essentially good agreement with the reported J values deduced from magnetic susceptibility data on trigonal oximato-bridged Mn(3) SMMs. VBCI is used to understand and analyze the DFT results. It is shown that the exchange coupling in these systems is governed by a spin-polarization mechanism inducing a pronounced and dominating ferromagnetic exchange via the oximato bridge as opposed to kinetic exchange, which favors a weaker and antiferromagnetic exchange via the bridging oxide. In the light of these results, a discussion of the exchange coupling in the Mn(6) family of the SMM with a record demagnetization barrier is given. 相似文献
80.
A combination of optical feedback self-locking of a continuous-wave distributed feedback diode laser to a V-shaped high finesse cavity, laser phase modulation at a frequency equal to the free spectral range of the V-cavity and detection of the transmitted laser beam at this high modulation frequency is described for the possible application in cavity-enhanced absorption spectroscopy. In order to estimate the noise level of an absorbance baseline, the triplet of frequency modulated light, i.e. the central laser frequency and the two sidebands, were transmitted through both the V-cavity in open air and a 1.5-cm long optical cell placed behind the cavity output mirror and filled with acetylene (C2H2) at low pressure. The performance of the setup was evaluated from the measured relative intensity noise on the cavity output (normalised by the bandwidth) and the frequency modulation absorption signals induced by C2H2 absorption in the 1.5-cm cell. From these data, we estimate that the noise-equivalent absorption sensitivity of 2.1 × 10?11 cm?1 Hz?1/2—by a factor of 11.7 above the shot-noise limit—can be achieved for C2H2 absorption spectra extracted from the heterodyne beat signals recorded at the transmission maxima intensity peaks of the successive TEM00 resonances. 相似文献