共查询到20条相似文献,搜索用时 93 毫秒
1.
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
2.
The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m1c with stress S along the [001] direction. The effect is most strongly observed at low electron densities ns. For and ns~2 × 1011cm-2 we obtain instead of the expected 0.2m0. Along with this change of a strong narrowing of the resonance is noted. Raising the temperature gives an additional ns- dependent increase of . 相似文献
3.
Electron and hole-drift velocity is measured in the layer semiconductors HgI2, GaSe, PbI2 and GaS, mainly on the direction parallel to the c-axis between 80 and 400 K. In the electric field range in question, electron and hole-drift velocity is proportional to the field except in the case of GaS, where a superohmic behaviour is observed. At 300 K the mobility parallel to the c-axis is , for HgI2; , for GaSe; , for PbI2. The highest hole mobility observed in GaS is .Where it is possible to compare these data with mobility values perpendicular to the c-axis, the three-dimensional character of the energy bands near the fundamental gap is proved.For HgI2 and GaSe we find no evidence for the large anisotropy of charge-carrier transport properties usually attributed to layered semiconductors. The mobility-temperature dependences found are interpreted on the basis of polar and non-polar optical phonon scattering mechanisms, except in the case of GaS, where a trapping model is used. The effective masses of electrons and holes are reported for PbI2 and, for the first time, for HgI2. 相似文献
4.
A continuous metal-nonmetal transition is observed in solid ArLa mixtures. The d.c. conductivity σ starts at a La atomic fraction cLa ? 0.15 with and increases exponentially with cLa until σ reaches the minimum metallic conductivity at cLa ? 0.4. The temperature dependence of σ shows variable range hopping between localized states for c>La ? 0.4 and metallic behaviour for 相似文献
5.
Dependence of static dielectric susceptibility and correlation length of charge density waves (CDW) with weak defects on parameter of incommensurability with lattice is investigated. In almost commensurate phase (h?hchc), and Rc ~ (h ? hc). In. Far from commensurability , , where a is the dimensionless ratio of random potential intensities, corresponding to backward and forward scattering impurities. 相似文献
6.
We present approximate analytic calculation of the functional derivative , where Tc is the superconducting critical temperature and is the electron-phonon spectral function, within the “square-well model” for the phonon mediated electron-electron interaction and weak coupling limit is the Debye energy). It is found that where λ is the familiar electron-phonon coupling parameter and is a universal function of the reduced frequency . We compare this formula with accurate numerical results for several weak coupling superconductors. The overall agreement is good 相似文献
7.
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
8.
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
9.
It is proved that the quantum mechanical Hamiltonian for bosons (resp, fermions) is bounded from below if N ≤ cbκ?1 (resp. ). H is unbounded from below if N ≥ cblκ?1 (resp. ). The constants cb and cbl (resp. cf and cfl) differ by about a factor 2 (resp. 4). 相似文献
10.
D. Stauffer 《Solid State Communications》1976,18(4):533-535
Usual theories for time-dependent effects in superparamagnetism (over-turning of large spin clusters) assume a flip rate ∝ exp (-U/kT). Instead, following Lifshitz and Kagan, we calculate the flip rate due to quantum-mechanical zero-point motion. The resulting “zero temperature” flip rate is R0 exp (-cn) for a cluster with n spins. R0 and c depend on domain wall energy and mass; typically, and c = 1. 相似文献
11.
R.C. Fernow S.W. Gray A.D. Krisch H.E. Miettinen J.B. Roberts K.M. Terwilliger W. DeBoer E.F. Parker L.G. Ratner J.R. OFallon 《Physics letters. [Part B]》1974,52(2):243-246
The elastic cross section for proton proton scattering at 6 was measured using a 70% polarized beam and a 75% polarized target at the Argonne ZGS. In the range we obtained small error measurements for the ↑↑, ↓↓ and ↑↓ initial spin states perpendicular to the scattering plane. At P⊥2 = 0.5 we also measured the recoil spin and found that the 5 different cross sections were very unequal. 相似文献
12.
Infrared hole burning within the absorption profile of the ν17 vibrational transition of 1,2-difluoroethane matrix-isolated in solid Ar, Kr, and N2 was observed. These measurements allowed the determination of the homogeneous and inhomogeneous linewidth ( at 2.5 K in Kr, ). The temperature dependence of the homogeneous linewidth is explained in terms of vibrational relaxation as well as dephasing processes. A detailed analysis of the changes in the absorption profile with irradiation and calculation of the potential energy surface for rotation of the molecule in the matrix cage suggest a reorientation of the molecules in the matrix to be the cause of the observed hole burning. 相似文献
13.
14.
C.R. Leavens 《Solid State Communications》1976,19(4):395-397
The Eliashberg gap equations relate the transition temperature Tc of an isotropic superconductor to its electron-phonon spectral function α2F(ω) and Coulomb pseudopotential parameter . Recently the Eliashberg theory has been used to derive some supposedly rigorous results bearing on the problem of attaining higher superconducting transition temperatures: Bergmann and Rainer derived an expression for the functional derivative ; Allen and Dynes showed that in the asymptotic limit of very large and Leavens proved that for any isotropic superconductor kBTc ?0.2309A, where A is the area under its electron-phonon spectral function. In this letter we show that the result of Allen and Dynes is not compatible with the other results and is, in fact, incorrect. 相似文献
15.
《Journal of Physics and Chemistry of Solids》2004,65(8-9):1381-1390
16.
We have determined the behavior of the density of states in the mixed state of superconducting alloys for T → Tc. The local density of states tends towards the BCS expression with the order parameter playing the role of the energy gap. The singularities are smeared out by the spatial average. The effective normal core radius of a vortex diverges like for T → Tc unlike the coherence length which diverges like . 相似文献
17.
《Physics letters. A》2002,305(5):231-238
With the help of complexifying a five-parameter exponential-type potential model, we obtain a general complex version of the Pöschl–Teller II potential, , where qc=q0e2iαε, real V1>0, q0>0 and . It has been shown that this complex potential is P-pseudo-Hermitian and PT-symmetric, where the parity operator P acts on the position operator as . The discrete energy eigenvalues are shown to be real when while they are complex conjugate pairs if . 相似文献
18.
We measured the magnetic susceptibility of KC24 from 4.2 to 300 K and found no anomalies near the phase transitions at 95 and 123 K as observed in the resistivity. We conclude that the transitions must be due to order- disorder transitions of the K atoms and not charge density wave formation. The susceptibility is anisotropic; at room temperature and . This anisotropy is not understood in terms of simple rigid band extensions of the band structure of graphite. 相似文献
19.
We studied the energy width and the width in reciprocal space Δq of the central mode of SrTiO3 above Tc. At Tc+4° we observed an energy width of about 6×10?7 eV. If the measured Δq is interpreted by a correlation length we obtain . 相似文献
20.
O.V. Nielsen T. Johansson L.M. Holmes G.J. Cock L.W. Roeland A.A. Ballman 《Journal of magnetism and magnetic materials》1976,1(4):320-325
The magnetic properties of MnNb2O6 single crystals have been studied in the temperature range 1.6–300 K (TN = 4.4 K), in fields up to 220 kOe. The high field saturation at low temperature, as well as the paramagnetic susceptibility at high temperature, agree well with a state for Mn2+ ions. From 1.6 to 3.8 K a spin flop is induced by fields ranging from 17 to 21 kOe, applied in the direction of the a-axis. Elements of the magnetic susceptibility tensors up to rank 12, measured below the spin flop field, are in accordance with a magnetic anisotropy originating mainly from magnetic dipolar interactions. 相似文献