共查询到20条相似文献,搜索用时 15 毫秒
1.
Spin lattice relaxation T1 of naturally abundant 13C nuclei in squaric acid was measured close to the antiferroelectric-paraelectric phase transition temperature Tc = 373 K. A rapid increase in is observed close to Tc coming from above, which follows the power law where . This behaviour is explained on the basis of the two-dimensional character of the fluctuations. 相似文献
2.
Anil K. Bhatnagar B. Bhanu Prasad N. Ravi R. Jagannathan T.R. Anantharaman 《Solid State Communications》1982,44(6):905-909
Amorphous Fe40Ni40B20 (VITROVAC 0040) alloy has been investigated using 57Fe Mössbauer Spectroscopy. The Curie temperature Tc is found to be well defined and is 695 ± 1 K. The quadrupole splitting just above Tc is 0.64 mm sec?1. The crystallization temperature is 698 ± 2 K, close to but definitely above Tc. The average hyperfine field Heff(T) of the glassy state shows a temperature dependence of indicative of the existence of spin wave excitations. The values of and are found to be 0.40 and 0.06, respectively, for T/Tc ? 0.72. At temperatures close to Tc, Heff(T) varies as (1 ? T/Tc)β where β is one of the critical exponents and its value is found to be 0.29 ± 0.02. 相似文献
3.
Optical absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for band in Ni2+ and band in Co2+ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm-1 in the case of Ni2+ at low temperature has been interpreted to be the superposition of vibrational mode of SO2-4 radical on band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ. 相似文献
4.
We report the result of the Co59 nuclear spin-lattice relaxation time T1 measurements in the diamagnetic monoboride CoB. The analysis of the data, in the 4.2–300 K temperature range, allows us to separate three contributions to the relaxation rate: first a Korringa process, (T1KT)?1= 0.21 sec?1K?1 (in good agreement with the temperature independent isotropic Knight shift) from which we deduced the Co59 hyperfine constant A=6.2 ×10?6eV, second an impurity contribution independent of temperature and third a quadrupolar term, , which is predominant at high temperature and well explained by the Van Kranendonk theory. It seems that it was the first time that such a quadrupolar effect was detected in a metallic compound. A remarkable coherency between Lundquist's three bands model and our experimental results has to be noted. 相似文献
5.
Kiyoshi Fuda Kohji Kishio Shigeru Yamauchi Kazuo Fueki 《Journal of Physics and Chemistry of Solids》1985,46(10):1141-1146
The 17O NMR measurement was made to elucidate the microscopic nature of vacancy motion in Y2O3-doped CeO2. Spin-lattice relaxation rate, T?11, spin-spin relaxation rate, T?12, and resonance intensity were measured at v0 = 8.13 MHz as a function of temperature [385 < T (K) < 1110] and composition []. The static electric field gradient associated with lattice defects resulted in the composition dependences of the line width and the intensity. In low dopant concentrations, doubly peaked temperature dependence of T?11 was found, while a single and asymmetric peak was observed in high concentrations. T?11 of 4.0 and 6.0 doped samples were analyzed using a barrier height distribution model for the oxygen vacancy jump. The mean value of the activation energy was found to increase with the Y2O3 concentration. 相似文献
6.
V Malathy Devi B Fridovich G.D Jones D.G.S Snyder 《Journal of Molecular Spectroscopy》1983,97(2):333-342
Line strengths and self- and nitrogen-broadened half-widths were measured for spectral lines in the ν3 and ν2 + ν4 bands of 12CH4 and 13CH4 from 2870–2883 cm?1 using a tunable diode laser spectrometer. From measurements made over a temperature range from 215 to 297 K, on samples of 12CH4 broadened with N2, we deduced that the average temperature coefficients n, defined as , of the Lorentz broadening coefficients for the ν3 and ν2 + ν4 bands of 12CH4 were 0.97 ± 0.03 and 0.89 ± 0.04, respectively. A smaller increase is observed in line half-width with increasing pressure for E-species lines, for both self- and nitrogen-broadening, than for other symmetry species lines over the range of pressures measured, 70 to 100 Torr. 相似文献
7.
The absorption and MCD spectra of the , , and spin-allowed transitions of Cr3+ in K2NaGaF6 are reported. It is shown that transitions to the . states are induced by T1u vibratio the other spin-allowed transition, , there are three competing intensity mechanisms: electric dipole induced by T1u vibrations, electric dipole induced by T2u vibrations and magnetic dipole, and an estimate is made of the relative importance of these. The magnetic dipole zero-phonon line is observed to be accompanied by a vibrational sideband for which the coupling is predominantly with T2u vibrations. Other weak transitions are observed in MCD spectra and their origin briefly discussed. 相似文献
8.
Mössbauer emission spectra of a frozen aqueous solution of 57CoCl2 show contributions from the and the Zeeman levels of Fe3+ ions at T = 4.2 K in H ? 30 kG. The K-capture results in a non-equilibrium state of relaxation time comparable to the lifetime of the nuclear excited state (~ 10?7 s). 相似文献
9.
Polycrystalline samples of the solid solution [(NH4)xK1?x]2SnCl6(0?x? 1) have been investigated by DSC, X-ray diffraction and Raman scattering experiments. Substitution of K+ by NH+4 depresses the phase transition temperature T1. For 0? x ?0.05 a linear temperature coefficient % is obtained. The cubic lattice constant roughly obeys Vegard's law, whereas the linewidth of the SnCl62?F2g internal vibration displays a nonlinear dependence on composition. 相似文献
10.
A.X. Cao S. Krichene G. Hauret J.P. Benoit J.P. Chapelle 《Solid State Communications》1982,43(12):933-936
The C33 constant is discontinuous for the lock-in transition at T1 = 169 K. The variation ΔT1 of the temperature of transition is a linear function of the applied electric field E and we find .Above a mean field E = 10 kV cm?1 the transition observed for a first heating spreads on several degrees because damages appear in the incommensurate phase and the electric field becomes inhomogeneous.The results obtained at low fields are in very good accordance with the value of calculated from the Clapeyron formula.Taking into account of the incommensurability of the phase above T1, it can be shown that The knowledge of the spontaneous polarisation P0 gives for the Curie constant C = 2.1 × 103 K in qualitative agreement with the value deduced from measurements of the dielectric constant in the ferroelectric direction. 相似文献
11.
Comparison between experimental absorption due to the transition of substitutional Ni2+(d8) in GaP and theoretical predictions based on the Jahn-Teller model is presented. Numerical solution of the Hamiltonian, in which spin-orbit interaction and T2-mode Jahn-Teller coupling are included, is in very good agreement with the energy position and intensities of the observed absorption lines. 相似文献
12.
EPR of 61Ni+ doped CuGaS2 at 4.2 K leads to the following experimental data: . High axial field splitting of 2T2 state stabilizes the center against Jahn-Teller interaction. Covalency reduction factor k is 0.76. 相似文献
13.
The nucleus 11B has been studied over the excitation energy range from 8.5 MeV to 21.5 MeV with the 9Be(3He, p)11B / reaction at / E3He = 38 MeV. The analogs of the parent states in 11Be have been located at 12.56, 12.92, 14.40, 16.44, 17.69, 18.0, 19.15 and 21.27 MeV. A complementary measurement with the 9Be(α, d)11B reaction at Eα = 48 MeV demonstrates that the 16.44, 17.69, 18.0 and 19.15 MeV resonances have rather pure isospin . The 14.40 MeV state is a strongly isospin-mixed analog of the state in 11Be. It is argued that spin S = 1 transfer is involved in the excitation of the 16.44 MeV state and its 3.887 MeV parent in 11Be in a two-step stripping process. The states and the lowest three states are compared with the predictions of DWBA utilizing shell-model form factors. It is concluded that the strength is more strongly fragmented than is implied by the calculations of Teeters and Kurath. 相似文献
14.
The emission of Ni2+ ions in MgO, KMgF3, KZnF3 and MgF2 crystals has been investigated. The fine structure on the bands at about 20 000 cm-1 and 13 000 cm-1 has been studied in detail and from this and the excitation spectra these bands are assigned to and transitions respectively. 相似文献
15.
The Curie-Weiss constant θ of the quasi b.c.c., , Heisenberg ferromagnets, (NH4)2 Cu Br4 · 2H2 O and Rb2 Cu Br4 · 2H2 O, have been derived from measurements of the susceptibility in the paramagnetic region (4.2 < T < 100 K) and of the high-field magnetization curves at . The values obtained point to the presence of further neighbour interactions considerably stronger than previously assumed. The effective number of equivalently interacting magnetic neighbours is estimated to be at least seventeen. 相似文献
16.
N.B. Manson J.T. Gourley E.R. Vance D. Sengupta G. Smith 《Journal of Physics and Chemistry of Solids》1976,37(12):1145-1148
At helium temperatures two sharp lines at 9350 and 9510 cm?1 have been observed for the first tune on the low-energy side of the broad double-peaked absorption corresponding to the transition in Fe2+ at the octahedral site in MgO. The lower energy line has a half width of 4 cm?1; Zeeman measurements show that it is of magnetic dipole origin. The Zeeman spectra are consistent with those expected for a pure electronic transition from the (5T2g)T2g ground state to the 5Eg excited state. The second line, with a halfwidth of ~ 35 cm?1, a vibrational sideband. 相似文献
17.
The magnetic structure of manganous acetate Mn(CH3COO)2, 4H2O has been solved by neutron diffraction. Manganous acetate crystallizes in the space group with Z = 6. Manganese atoms (in position 2a and 4e) are located in (100) planes. Below TN = 3.18 K this compound is antiferromagnetic in a zero applied field with the k vector [ 00]. The plane (100) is ferromagnetic. The magnetic group is . 相似文献
18.
The 58Ni(τ, α)57Ni reaction has been studied at 25 MeV incident energy. Angular distributions have been measured from 5° to 50° with a split-pole spectrometer up to 13.5 MeV excitation energy. A local zero-range DWBA analysis has been carried out, allowing l-assignments for about eighty levels, most of them previously unknown. An isospin-dependent potential has been used in the calculation of the neutron form factor for both T<and T> states, and the C2S values deduced using this procedure are compared to those obtained with the usual separation energy method. Analog states of eleven 57Co levels have been identified and the eventuality for isospin mixing in 57Ni has been discussed. A sum rule analysis has been carried out and energy centroids of hole states have been determined. About 60% of the strengths and the full and hole strengths are observed. It is shown that the two excess neutrons in the 58Ni ground state mainly populate the orbitals, whereas the occupancy number of the subshell is found to be smaller than 0.1%. Some non-pickup angular distributions have also been observed and a CRC analysis assuming two-step processes in the (τ, α) reaction and weak-coupling wave functions for final states has been attempted. Assignments of Jπ values are proposed for four 57Ni levels, based on this analysis. 相似文献
19.
Electron spin resonance relaxation times were measured for the radiation induced radical ion SeO43? in selenium doped KDP single crystals. The spin-lattice relaxation time was found to obey the relation from 7 K to 200 K except in the neighborhood of the transition temperature where the data fit the expression T1?1 = T1R?1b±T ? Tcm± where θ is the Debye temperature and the plus and minus signs refer to data at temperatures above and below Tc respectively. 相似文献
20.
Antifluorite type solid electrolytes, Li2+x-y-z[(NH)1-x-y-zNxClyHz] have been synthesized from Li3N, LiCl and LiCl·H2O or ]. Either of the last two compounds introduces NH2- ions into the product and is indispensable to form the antifluorite type structure. The lattice parameter decreases with increasing amount of NH2- ions in the compound, reflecting the difference of anion sizes between Cl- and NH2- ions. Activation energies of Li+ diffusive motion, derived from both conductivity and NMR measurements, increase with concentration of NH2- ions, although the values differ by a factor of ≈2 netween the both methods. 相似文献