共查询到20条相似文献,搜索用时 15 毫秒
1.
Kenji Kojima Kusuo Nishiyama Kanetada Nagamine Hironobu Ikeda 《Hyperfine Interactions》1993,78(1-4):429-433
The site diluted finite spin cluster system Rb2CO
x
Mg1–x
F4 (x=0.15, 0.4, 0.5) has been investigated by the +SR technique. Muon spin relaxation was observed in these diluted magnetic systems in a weak longitudinal field of 100 G. By reducing temperature below 100 K, the experimental data show features of slowing down phenomena of the Co electron moments in the finite spin clusters. 相似文献
2.
A.J. Bouvier D. Inard V. Veyret B. Bussery R. Bacis S. Churassy J. Brion J. Malicet R.H. Judge 《Journal of Molecular Spectroscopy》1998,190(2):189-197
The analysis of the rotational structure of the high-resolution Fourier transform 000absorption spectrum of the3A2←X1A1band system of the “Wulf” transition of the isotopomer16O3of ozone is reported for the first time. With a near pure case (b) coupling model for the upper triplet state, we have assigned a significant portion of the spectrum, mainly theF1(J=N+ 1) andF2(J=N) spin components, primarily in the lower frequency region of the band. The lines corresponding to theF3(J=N− 1) component are weak at lower frequencies and heavily congested in the central and higher frequency regions of the spectrum. Perturbations and predissociation phenomena have reduced the effective lifetime of the metastable3A2state and have also limited the number of transitions included in the least-squares fit of the band. Approximately 100 lines have been assigned in the range from 9100–9550 cm−1. Three rotational, three centrifugal distortion, three spin–rotation, and one spin–spin constant were varied. The geometry of the molecule in the3A2state, as determined from these constants, isr= 1.345 Å and θ = 98.9°, in good agreement withab initioresults. 相似文献
3.
The technique of multiple-quantum J-resolved NMR spectroscopy (MQ-JRES) is introduced and applied to the spin system SI3–M (such as in the example given here, the 13CH3–12CH in alanine). The SI3 spin system was excited to its highest quantum state (8SyIxIyIy), which consists of four coherences: quadruple quantum of (3I + S), double quantum of (3I − S), double quantum of (I + S), and zero quantum of (I − S). In the MQ spectrum generated from the projection onto the F1 dimension, the resonances of the different multiple-quantum coherences are resolved by their coupling constants to the remote spin (M). The absorptive lineshapes in both F1 and F2 dimensions enable accurate measurements of transverse relaxation rates, and both amplitude and relative signs of the long-range coupling constants are to be derived from either frequency or time domain data. The selective detection of MQ-JRES spectra of the individual MQ coherences using either phase cycling or pulsed field gradients is presented. 相似文献
4.
Polycrystalline Nd1−xKxMnO3 (x=0.10–0.20) compounds have been prepared in single phase form with Pbnm space group. The magnetic properties were studied by measuring dc magnetization and ac susceptibility. They exhibit paramagnetic to ferromagnetic transition with transition temperature ranging from 116 to 128 K. The magnetization data have been analyzed by using Brillouin function model and by taking into account the ferromagnetic interaction. The effective spin contribution towards ferromagnetic interaction and spin canting angle have been estimated. The spin canting angle is found to decrease with increase in doping. Magneto-caloric effect (MCE) has been studied and the maximum change in entropy was found to be 1.76 J/kg K for 1 T field. Metal–insulator transition and colossal magnetoresistance of the order of 60% for 1 T field have been observed for x=0.20 sample. 相似文献
5.
In this paper the density, electrical conductivity, and dielectric permittivity of vacant ceramics of Ca
x
Th1–x
O2–x
and Y
x
Th1–x
O2–x
/2 type, respectivelly, were investigated as functions of temperature, frequency, and composition of these systems.The density drops with increasing calcium or yttrium amount, respectively. In the ThO2-CaO system this is in agreement with the mechanism of formation of vacant phase Ca
x
Th1–x
O2x
. The decrease of porosity in the ThO2-Y2O3 system with increasing yttrium content can be due various factors which influence the mobility of Y3+ ions and, thus, also the formation of pores.The investigation of transport numbers has shown that whilst the Ca
x
Th1–x
O2–x
phase under our experimental conditions is essentially p-type conductor, the Y
x
Th1–x
O2–x/2 phase is essentially ionic conductor.The transport of ion carriers is a diffusion-like process which has activation energy 1·28 to 1·16eV in the Ca
x
Th1–x
O2–x
phase and 1·28 to 1·06 in the Y
x
Th1–x
O2–x
/2 phase, respectively. The association of impurity ions with anion vacancies provides the maxima in conductivity isotherms.The relative dielectric permittivity of the vacant phase Ca
x
Th1–x
O2–x
ranges from 19·2 to 36·2, in the phase Y
x
Th1–x
O2–x
/2 from 19·2 to 103, depending on temperature, frequency, and composition of these systems. 相似文献
6.
Ken-ichi Kumagai Kenji Kawano Kenji Fujiwara Isao Watanabe Kusuo Nishiyama Kanetada Nagamine 《Hyperfine Interactions》1993,79(1-4):929-935
Muon spin rotation (SR) is applied to La2–x
Ba
x
CuO4 aroundx=0.12 where the superconductivity (SC) is suppressed remarkably. The magnetic ordering of Cu-moments appears below 35 K in the narrow range ofx where a lattice instability from the low temperature orthorhombic (LTO) to the low-temperature tetragonal (LTT) structure exists. The present study suggests strongly that the magnetic ordering of Cu-moments is an important factor in the suppression of high-T
c superconductivity aroundx=0.12 in La2–x
Ba
x
CuO4. Similar results are obtained for the La2–x
Sr
x
CuO4 and La2–x–y
Sr
x
Nd
y
CuO4 systems. 相似文献
7.
The magnetostatic properties of K2Co
x
Fe1–x
F4 have been investigated by susceptibility and Mössbauer measurements at different concentrations and temperatures. Three magnetically ordered phases are found: a planar phase, an OAF phase, and an uniaxial phase. The experimental results are compared to a molecular-field calculation. At certain concentrations and temperatures it is not possible to obtain a good least squares fit of the Mössbauer spectra, which is tentatively assigned to relaxation effects due to fast spin fluctuations at the OAF phase transition. 相似文献
8.
A. N. Aleev V. A. Arefiev V. P. Balandin V. K. Berdyshev V. K. Birulev A. S. Chvyrov I. I. Evsikov T. S. Grigalashvili B. N. Gus'kov I. M. Ivanchenko et al. 《Czechoslovak Journal of Physics》1990,40(11):1216-1225
A signal of the-K+K– decays has been observed in neutron-hydrogen interactions at energies of 30–70 GeV in an experiment using the BIS-2 spectrometer. The longitudinal momentum spectrum in the forward region,x
F<0·1 atp
T<1 GeV/c, can be well described by a power law dependence (1–x
F)N withN=4·28±0·42. Thep
T
2
-spectrum has been parametrized by the exp(–Bp
T
2
) law with the exponentB=(3·02±0·55) (GeV/c)–2. The extrapolation of the measured cross section to the full kinematic region yields a value of (220±85) b in agreement with measurements from the proton beams. 相似文献
9.
Zhao Min-Guan Zhao Xiao-Ning Zeng Xiao-Lan 《Zeitschrift für Physik B Condensed Matter》1988,72(3):353-355
Various superconductivity mechanisms show that the electron pair is in spin singlet (S=0) belowTc. In contrast with these, our EPR measurements show that the electron pair is in spin triplet (S=1) rather than the spin singlet. Since an intense zero field absorption was observed in the high temperature superconductors of YBa2Cu3O7–y
, and YBa2Cu3O7–y
F1, which violated various spin-pairing singlet superconductivity mechanisms. 相似文献
10.
M. M. Hasegawa E. A. de Andrada e Silva G. C. La Rocca 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):400
It is shown that, due to the electron–hole symmetry of the fundamental gap of the lead–salts (PbTe, PbSe and PbS), the Rashba spin splitting in their flat band asymmetric quantum wells is much reduced with the usual equal conduction and valence band-offsets. Different from the III–V case, we find that the important structure inversion asymmetry for the Rashba splitting in IV–VI quantum wells with different left and right barriers is not a material property (i.e., barrier height, effective mass or band gap) but results from the band alignment. This is shown by specific envelope function calculations of the spin-dependent subband structure of Pb1−xEuxTe/PbTe/Pb1−yEuyTe asymmetric quantum wells (x≠y), based on a simple but accurate four-band kp model for the bulk band structure near the gap, which takes into account band anisotropy, nonparabolicity and multi-valley effects. 相似文献
11.
Several solid solutions of the mixed crystalline Fe1–x
V
x
F3 series, synthesized by the solid-state reaction, are investigated by Mössbauer spectroscopy. The evolution of the hyperfine structure as a function of temperature suggests that the Fe0.50V0.50F3 compound exhibits a spin-clustering phenomenon over the temperature range 70–175 K. We report here some preliminary high field Mössbauer spectra in order to discuss the magnetic behaviour. 相似文献
12.
The magnetic susceptibility and magnetization are presented for polycrystalline samples of the alloy systems Cd1-xMnxTe 0 < x 0.1 and Sn1-xMnxTe 0 < 4 0.4. The magnetic measurements were performed between 2.3 K and 300 K in external magnetic fields up to 11 kOe. At sufficiently high temperatures the susceptibility can be described by a Curie-Weiss law. In the system Sn1-xMnxTe θp is positive. A linear dependence θp ∞ x was found with θp(0.4) = 49 K. In the series Cd1-xMnxTe θp changes sign. For θ < x < 0.04 θp is positive with a maximum θp ≈ 10 K at x = 0.02. In the region x #62; 0.04 θp becomes negative with θp = -35 K at x = 0.1. The effective spin value of manganese is Seff #62; 5/2 for all the samples. The investigation was done to check the assumption that ferromagnetic coupling may exist in tellurides of manganese if the shortest distance dMnMn is greater than 3.4 Å. This hypothesis has been stated. In the case θp #62; 0 the results are partly explained by the RKKY exchange coupling. 相似文献
13.
I. O. Troyanchuk L. S. Lobanovsky D. D. Khalyavin S. N. Pastushonok H. Szymczak 《Journal of magnetism and magnetic materials》2000,210(1-3)
A systematic study of the doping of the Mn-sites by cobalt in three series of manganites — La0.76Ba0.24(Mn1−xCox)O3 single crystals, La2/3Ba1/3(Mn1−xCox)O3 and La(Mn1−xCox)O3 ceramics has been performed. It was found that La(Mn1−xCox)O3 annealed at 800°C in the range 0.4x0.9 is a mixture of ferromagnetic domains with ordered Mn and Co ions and ionically disordered spin-glass domains. In the quenched samples the fraction of spin-glass-type component increases strongly. The La2/3Ba1/3(Mn1−xCox)O3 solid solutions exhibit also an evidence for phase separation in the range 0.5x0.8. All the La(Mn1−xCox)O3 samples show an insulating behavior, however, magnetoresistance reduces strongly when the cobalt content rises to x=0.5. The La0.76Ba0.24(Mn1−xCox)O3 single crystals show first-order phase transition below their Curie points associated with a change of ground state of the Co2+ ions. The magnetic phase diagrams are depicted. The results are discussed in terms of positive Mn3+–O–Mn4+, Mn3+–O–Mn3+, Mn4+–O–Co2+ and negative Mn4+–O–Mn4+, Co2+–O–Co2+, Co2+–O–Mn3+ superexchange interactions as well as Co2+ and Mn4+ ionic ordering. 相似文献
14.
Vasil'ev A. D. Vorotynova O. V. Martynov S. N. Petrov S. B. Rudenko V. V. Sudakov A. N. 《Russian Physics Journal》2001,44(7):708-711
Measurements of the electron paramagnetic resonance (EPR) of Fe3+ ion pairs in InBO3 crystals are conducted. Some parts of the procedure of spectrum identification without measuring the temperature dependence of the resonant line intensities have been developed. Experimental curves of the second- and fourth-order axial Hamiltonian constants D
S and (a – F)S, respectively, of the total spin number S are constructed. The single-ion second-order axial constant D
c is well described by a linear dependence on S. The constant (a – F)S has a quadratic dependence. 相似文献
15.
Pei Ding Erjun Liang Mingju Chao Xinyong Guo Jingwei Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):654-659
Aligned CNx nanotubes were fabricated by pyrolyzing ethylenediamine on p-type Si(1 1 1) substrates using iron as the catalyst. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrum (XPS) and Raman spectroscopy were used to characterize the CNx nanotubes. The CNx nanotubes with the average length of 20 μm and diameters in the range of 50–100 nm have the “bamboo-like” structure and worse crystalline order. The low-field emission measurements of the CNx nanotubes indicated that 20 μA/cm2 current densities were observed at an electric field of 1.4 V/μm and 1.280 mA/cm2 were obtained at 2.54 V/μm. The CNx nanotubes exhibit better field emission properties than the carbon nanotubes and the BCN nanotubes. The emission mechanism of CNx nanotubes is also discussed. 相似文献
16.
Near-infrared photorefractivity in Cr-doped potassium sodium strontium barium niobate single crystal
J. Bergquist Y. Tomita M. Shibata 《Applied Physics A: Materials Science & Processing》1992,55(1):61-64
We report on the photorefractive properties of a Cr-doped (K1–x
Na
x
)2A–2 (Sr
y
Ba1–y
)2–A
Nb10O30 (x=0.586, y=0.659, A=1.12) single crystal in the near-infrared spectrum. The sample exhibits photorefractivity for wavelengths up to at least 840 nm where the steady-state two-beam coupling gain is found to be larger than 2 cm–1. Photorefractive gain and decay rate are measured as a function of wavelength, grating spacing and intensity. The wavelength dependence of gain fluctuations in two-beam coupling are also measured. 相似文献
17.
《Physics letters. [Part B]》2001,520(3-4)
A measurement of the derivative (∂ lnF2/∂ lnx)Q2≡−λ(x,Q2) of the proton structure function F2 is presented in the low x domain of deeply inelastic positron–proton scattering. For 5×10−5x0.01 and Q21.5 GeV2, λ(x,Q2) is found to be independent of x and to increase linearly with lnQ2. 相似文献
18.
Zn1−xCoxO films were grown on glass by sol–gel spin coating process. The Zn1−xCoxO thin films with 10 at.% Co were highly c-axis oriented. The electrical resistivity of the films at 10 at.% Co had the lowest value due to the highest c-axis orientation. XPS and AGM analyses indicated that Co metal clusters weren’t formed, and the ferromagnetism was appeared at room temperature. The characteristics of the electrical resistivity and room temperature ferromagnetism of sol–gel derived Zn1−xCoxO films suggest a potential application to dilute magnetic semiconductor devices. 相似文献
19.
P. Novák 《Czechoslovak Journal of Physics》1966,16(8):723-736
The anisotropy constants K1 for systems MnxFe3–xO4, with 1x 1·8, are calculated on the basis of the one-ion model and it is shown that the anomalous temperature dependence of the constant K1 can be explained by the presence of Mn3+ ions in octahedral positions. The influence of the spin order on the magnetic anisotropy and the uniaxial anisotropy in systems MnxFe3–xO4 are discussed. 相似文献
20.
Malmi P Punkkinen M Ylinen E Shevtsov V 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,145(2):326-333
Double quantum (DQ) filtering is shown to lead to an effective separation of the NMR signals from the para (I = 1) and ortho (I = 2) molecules in solid deuterium. The separation is achieved by the pulse sequence 90φ°–tpr–90φ°–tev–90x°–t, where the phase-cycled first two pulses create the DQ coherence. Two components are observed after the third pulse; the para signal shows the maximum at a short time t while the ortho signal reaches the maximum at a longer t. The observed signal can be expressed as
∑I [FI(tpr − t) − FI(tpr + t)], where FI(t) is a proper fitting function for the free induction signal of the para and ortho molecules (with I = 1 or 2, respectively). Numerical fits to experimental data at 4.2 and 2 K show that this method can be used to determine the ratio F1(0)/F2(0) and thus, because the initial value FI(0) is proportional to the respective magnetization before the pulse sequence, the ortho and para concentrations in solid deuterium. 相似文献