共查询到20条相似文献,搜索用时 15 毫秒
1.
E. Rastelli A. Tassi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):285-289
Dipolar spin-spin interactions play a crucial role as for the magnetic order in the compounds of the RBa2Cu3O6+x family, (R = Dy, Er, Nd). However, inelastic neutron scattering data observed in ErBa2Cu3O7 can be explained only if exchange interactions in addition to dipolar ones are taken into account.
Received: 12 January 1998 / Received in final form: 26 March 1998 / Accepted: 10 April 1998 相似文献
2.
The dispersion coefficients C6, C8 and C10 for the interactions between helium and helium-like ions in the metastable states of 2 1S and 2 3S with Z up to 10 are calculated using variational wave functions in Hylleraas coordinates. 相似文献
3.
J. Chrysochoos 《Journal of luminescence》1974,9(2):79-93
Photoexcitation of EuCl3.6H2O and TbCl3.6H2O mixtures in DMSO at various wavelengths brings about a decrease in the fluorescence intensity of Tb3+ and a subsequent enhancement in the fluorescence intensity of Tb3+ provided that [Tb3+] < [Eu3+]. The average value of the electronic excitation energy transfer rate constant k10 which was found to be independent of the excitation wavelength, was determined to be about 1.50 × 103 M-1 s-1. Photoexcitation of Tb3+ and subsequent population of high energy excited states is accompanied by rapid nonradiative de-excitation processes to the lowest excited state 5D4, which is the origin of the energy transfer process. A lower limit for the value of the reaction rate constant, associated with the transition 5D3 ? 5D4, namely k5, is of the order of 105 ?106 s-1. Excitation at conditions leading to the exclusive population of the 5D4 state of Tb3+ gave rise to a value of k10 equal to (2.2 ± 0.4) × 103 M-1 s-1 and a critical separation (R0)exp between Tb3+ and Eu3+ of about 13 Å. A theoretical value of R0 equal to 14.2 Å was calculated. The energy transfer process does not appear to take place via clear cut dipole-dipole interactions but rather via complex multipole and/or exchange interactions. 相似文献
4.
Hybrid polypyrrole (PPy)/α-Fe2O3 nanocomposite films were fabricated by spin coating on a glass substrate. X-Ray diffraction analysis revealed the crystalline structure of α-Fe2O3 nanostructures and the nanocomposites. The broad PPy peak weakened in intensity as the α-Fe2O3 content increased in PPy/α-Fe2O3 nanocomposites. Characteristic Fourier-transform IR peaks for pure PPy shifted to higher wavenumbers on addition of α-Fe2O3 to PPy/α-Fe2O3 nanocomposites. This can be attributed to better conjugation and interactions between PPy and α-Fe2O3 nanoparticles. Field-emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy images of the nanocomposites reveal a uniform distribution of α-Fe2O3 nanoparticles in the PPy matrix. UV-vis absorption spectroscopy revealed a blue shift from λmax= 441 nm for PPy to λmax= 392 nm for PPy/α-Fe2O3, reflecting strong interactions between PPy and α-Fe2O3 nanoparticles. The room-temperature dc electrical conductivity increased from 4.33×10−9 to 1.81×10−8 S/cm as the α-Fe2O3 nanoparticle content increased from 10 to 50 wt.% in PPy/α-Fe2O3 nanocomposites. 相似文献
5.
A. E. Mefed 《JETP Letters》1996,64(5):363-369
The longitudinal nuclear spin relaxation in an effective magnetic field H
e3 acting in a triply rotating coordinate system is recorded. Rotating and doubly rotating coordinate systems are employed for
strong suppression of the secular nuclear dipole interactions in the first two orders and for separation of higher-order interactions
(four-and five-spin). Experiments on protons in polycrystalline benzene showed that the contribution of such multispin dipole
interactions to this relaxation can be observed selectively as a pronounced local minimum in the temperature dependence of
the relaxation time. This contribution correponds to ultraslow molecular motions with rates ≃ γH
e3≃2π(101−103) s−1 and can be employed to study such motions in detail, including for purposes of identification of the form of the motion.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 335–340 (10 September 1996) 相似文献
6.
We have determined the temperature dependence of σ1 of 129Xe in oxygen gas. These results were obtained by measurement of the resonance frequency of 129Xe in gas samples of known densities in Xe and O2. The shift of the resonance frequency due to Xe-Xe interactions has been measured in pure Xe gas samples with improved precision. This allows the determination of σ1(Xe-O2) by subtracting out the known effect of Xe-Xe interactions in mixed Xe-O2 samples. σ1(Xe-O2) values are reported here for the temperature range 220 to 440 K. The values of σ1(Xe-O2) are adequately described by the polynomial function in p.p.m. amagat-1 σ1(Xe-O2) = - 1·061 + 3·64 × 10-3τ - 2·19 × 10-5τ2 + 9·58 × 10-8τ3 - 2·08 × 10-10τ4, where τ = (T - 300 K). It is found that the temperature dependence of σ1(Xe-O2) can be interpreted in terms of a contact interaction between Xe and the paramagnetic O2 molecule. 相似文献
7.
Crystal field parameters for Pr3+ in {[Ni(salen)Pr-(hfac)3](H2O)} (noted as NiPr) and {[Ni(salen)Pr(hfac)3(pyr)]-(CHCl3)} (noted as NiPrpyr) have been found from a fit to the thermal variation in the magnetic susceptibility of NiPr and NiPrpyr. The nature of exchange interaction in [Cu(salen)Pr(hfac)3(pyr)] (noted as CuPrpyr), {[{Cu(salen)Pr(hfac)3}2(pyz)](H2O)3} (noted as Cu2Pr2pyz) and {[{Cu(salen)Pr(hfac)3}2(bpy)]-(CHCl3)2} (noted as Cu2Pr2bpy, bpy=4,4_-bipyridine) have been found using the derived results for NiPr and NiPrpyr. All the exchange interactions give significant contribution to the thermal variation in magnetic susceptibility below 50 K. The contribution due to Pr-Cu interaction is positive while that of the Cu-Cu and Pr-Pr interactions are negative. The behaviors below 10 K for Pr-Cu and Pr-Pr are difficult to explain, and point to a possible change in structure of CuPrpyr, Cu2Pr2pyz and Cu2Pr2bpy below 10 K. The theoretical thermal variations in the magnetic specific heat of NiPr and NiPrpyr are computed and discussed. 相似文献
8.
Schrödinger operators on Sobolev spaces are considered as new solvable models with point interactions. A simple formula for the deficiency indices of a minimal Schrödinger operator with point interactions is given. Examples of point interactions on the space W21(
3) are constructed.Mathematical Subject Classification (2000). 37J10, 47A10 相似文献
9.
It is shown that, within the parton picture, weak (P-odd) effects increase with energy and momentum transfer. The presence of an effctive current with ΔS = 0 and 1 due to constituent interchange or annihilation is expected in the parton picture of hadron-hadron weak interactions. A typical value of P-odd effects, nucleon or hyperon polarization or asymmetry in quasi two-body reactions is about 10?4 at Elab ~ 103 GeV and 10?3 in large angle (t ~ s) scattering in the conventional current × current scheme of weak interactions. A principal possibility to clear up quark statistics is pointed out. 相似文献
10.
An updated analysis of the full NOMAD data corresponding to 1.35 × 106 charged current interactions has been performed to search for neutrino oscillations through ντ appearance. This document updates the recently published results on the νμ → ντ and νμ → νe oscillations search in NOMAD [1] with a unified analysis of the hadronic channels. 相似文献
11.
An atom (B) situated near a plane of atoms (A) experiences an interaction potential energy V = (V2 + V3 + … The leading term is the sum over the monlayer of 2-body interactions. We compute here the 3-body correction V3. Numerical results are presented for the case of noble gases, H and CH4. For H or He near a Xe layer, V3 reduces the well depth by ~ 10%. 相似文献
12.
ABSTRACT The geometry of the four-coordinated Sn atom in the title compound, (CH3)3Sn(C2H2N3S2), is distorted tetrahedral with three Sn–C bonds and one Sn–S bond. Two crystallographically distinct molecules a and b within the asymmetric unit are hydrogen bonded. Intermolecular “N–H?N” hydrogen bond interactions generate infinite 1D chains consisting of alternating, centrosymmetric R2,2(8) and R4,2(10) rings. 相似文献
13.
《Journal of luminescence》1986,36(2):109-113
Quenching of the room-temperature fluorescence excitation and emission spectra of indole, 3-carbinolindole, 5-methoxyindole, and 3-methylindole in dimethyl sulfoxide by trivalent lanthanide ions Ln3+ was interpreted in terms of dynamic interactions between (1La, 1Lb) states of indoles and Ln3+. The fluorescence lifetimes of these indoles vary from 5.3 to 8.4 ns, according to their structure. Quenching rate constants (kQ) range between 2.6×108 and 1.7×1010 M−1s−1. Values of kQ are significantly larger for Eu3+ and Yb3+ than for other lanthanide ions. 相似文献
14.
We have developed a technique for studying time dependent hyperfine interactions using selective excitation double Mössbauer (SEDM) procedures. The measured relaxation time between the two spin orientations of the iron atoms in α-Fe2O3 at the Morin transition is 1.1 ± 0.2 × 10-7 sec. 相似文献
15.
《The European Physical Journal C - Particles and Fields》2007,52(3):543-552
In this paper a search for associated charm production both in neutral and charged current ν-nucleus interactions is presented.
The improvement of automatic scanning systems in the CHORUS experiment allows an efficient search to be performed in emulsion
for short-lived particles. Hence a search for rare processes, like the associated charm production, becomes possible through
the observation of the double charm-decay topology with a very low background. About 130000 ν interactions located in the
emulsion target have been analysed. Three events with two charm decays have been observed in the neutral-current sample with
an estimated background of 0.18±0.05. The relative rate of the associated charm cross-section in deep inelastic ν interactions,
σ(cc̄ν)/σNC
DIS=(3.62+2.95
-2.42(stat)±0.54(syst))×10-3 has been measured. One event with two charm decays has been observed in charged-current νμ interactions with an estimated background of 0.18±0.06 and the upper limit on associated charm production in charged-current
interactions at 90% C.L. has been found to be σ(cc̄μ-)/σCC<9.69×10-4. 相似文献
16.
The anomalous magnetocaloric effect in singlet rare-earth paramagnets near energy level crossing has been experimentally observed for the first time. The magnetization and differential magnetic susceptibility of Ho1 ? x Y x VO4 crystals (x = 0, 0.5) measured along the tetragonal axis in a pulsed magnetic field with various change rates near the crossover field, dH/dt, from 3 × 103 to 2.5 × 102 T/s are compared to the data in static magnetic fields down to 0.1 K. These data indicate the large negative magnetocaloric effect in the pulsed magnetic field, so that the crystal with the initial temperature T 0 = 4.2 K is cooled much lower than 1 K. The experimental data are qualitatively described in the crystal field model with various interactions including hyperfine interactions and with the known interaction parameters. 相似文献
17.
G. A. Petrakovskii K. A. Sablina A. M. Vorotynov O. A. Bayukov A. F. Bovina G. V. Bondarenko R. Szymczak M. Baran H. Szymczak 《Physics of the Solid State》1999,41(4):610-612
The temperature dependence of the magnetic susceptibility of Cu3B2O6 single crystals grown by spontaneous crystallization from a melt consisting of a mixture of CuO and B2O3 and the behavior of their magnetization are investigated in magnetic fields up to 55 kOe. A broad susceptibility maximum
is observed near 39 K, and a sharp drop in susceptibility is observed at T<10 K. The paramagnetic Néel temperatures for all orientations of the magnetic field in the crystal investigated are negative,
attesting to the predominantly antiferromagnetic character of the exchange interactions. The effective magnetic moment of
the Cu2+ ion is anisotropic and lies in the range from 1.054μ
B to 1.545μ
B. The magnetization depends linearly on magnetic field at T>10 K, whereas at temperatures below 10 K a discontinuity is observed at fields of the order of 40 kOe. At room temperature,
electron magnetic resonance characterized by an almost isotropic g factor (g=2.165) is detected at 36.22 GHz. The exchange interactions in Cu3B2O6 are analyzed on the basis of the Goodenough-Kanamori rules. The possibility of the establishment of a singlet magnetic state
in the crystal is analyzed.
Fiz. Tverd. Tela (St. Petersburg) 41, 677–679 (April 1999) 相似文献
18.
The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm−1) on a Fourier transform instrument in the region 730 to 1170 cm−1 containing the perpendicular bands, ν9 and ν10. A total of 21 subbands with KΔK ranging from −6 to +14 have been assigned in the ν9 band, and 26 subbands with KΔK = −10 to +15 have been assigned in the ν10 band. The bands are affected by a combination of a Jz-Coriolis and a quartic anharmonic interaction between their upper states ν9 and ν10. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν9 and ν10 upper states. A set of spectroscopic constants for the ν9 and ν10 states and for some of the perturbing states is reported. 相似文献
19.
A. E. Mefed 《Applied magnetic resonance》2001,21(2):127-145
A method for measuring nuclear magnetic spin-lattice relaxation in solids in the effective field He3 acting in the triply rotating frame (TRF) is described. The method advances the previously described techniques whereby nuclear magnetic resonance and relaxation in the rotating (RF) and doubly rotating frames (DRF) are measured directly. In the present work, the RF and DRF are employed for suppressing the secular part of nuclear dipole-dipole (DD) interactions in the first two orders. As a result, the higher-order DD interactions (four- and five-particle ones) were separated, and their contribution to the nuclear spin-lattice relaxation in the TRF was studied experimentally. The experiments were carried out on protons in polycrystalline benzene. With the introduced technique, an overall spin-lattice relaxation decay in the TRF was recorded continuously during a single radio-frequency pulse with a length not exceeding 1 s. The contribution of multiproton nonsecular DD interactions to the proton spin-lattice relaxation in the TRF was observed selectively as a pronounced local minimum in the temperature dependence of the relaxation timeT 1ϱϱϱ. This contribution corresponds to ultraslow motion of benzene molecules with a rate about γHe3 ≈ 2π · (101-103) s-1 and is determined quantitatively by specific correlation functions corresponding to the multiparticle nonsecular DD interactions of protons. The prospects of using this method for studying ultraslow atomic and molecular dynamics in solids are discussed. 相似文献
20.
The half-life of the 58keV level of159Tb was determined by classical resonance absorption using the centrifuge technique and by Mössbauer spectroscopy measuring the natural line width and found to beτ 1/2=(58±10)ps. Mössbauer spectra for Tb and Tb2O3 absorbers and for Dy2O3 and GdFe2 sources were investigated for temperatures between 9 and 385 K. Results for hyperfine interactions and Debye Waller factors are given. The Debye Waller factors are compared with predictions obtained from other experimental results. 相似文献