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1.
The longitudinal and transverse relaxation rates of 19F nuclei in Pr2CuO4−x
Fx (x=0.20) samples are measured at high temperatures (150 K<T<600 K). A feature is found in the temperature dependence of the relaxation rates at temperature T′≅300 K. The magnetic properties of the electronic superconductor Pr2CuO4−x
Fx as a possible system with a stripe ordering of carriers and spins are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 328–332 (25 February 1997) 相似文献
2.
K. N. Mikhalev S. V. Verkhovskii A. P. Gerashchenko Yu. V. Piskunov A. Yu. Yakubovskii A. P. Rusakov 《JETP Letters》1999,70(5):346-351
The spin-lattice relaxation times T
1 in Ba1−x
KxBiO3 (x=0.3, 0.4, 0.5) were measured in the normal temperature range (20–300 K).A substantial contribution to the spin-lattice relaxation
rate from dynamic local distortions of the crystal lattice near potassium atoms is found. The activation energy of this process
increases with decreasing potassium concentration, and the frequency of lattice excitations decreases. The nature of the low-frequency
lattice dynamics is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 344–349 (10 September 1999) 相似文献
3.
The temperature dependences of the transverse V
t
and longitudinal V
l
sound velocities in single crystals of the perovskites La1−x
SrxMnO3 (x=0.1, 0.175, 0.2, 0.25) in the temperature interval T=70–350 K are investigated by the resonance method. Anomalies — small minima and kinks in the temperature dependences V
l
(T) and V
t
(T) — are observed at the Curie points. A strong jumplike increase (by up to 30%) in both the longitudinal and transverse sound
velocities, which attests to sizable hardening of the acoustic branches of the phonon spectrum, is observed near the temperatures
of the structural transitions between the rhombohedral and orthorhombic phases (for x=0.175, 0.2, 0.25) and at the phase transition to the polaron-ordered state (for x=0.1).
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 2, 141–146 (25 July 1998) 相似文献
4.
L. K. Aminov I. N. Kurkin S. P. Kurzin D. A. Lukoyanov I. Kh. Salikhov R. M. Rakhmatullin 《Journal of Experimental and Theoretical Physics》1997,84(1):183-189
Our studies involve measuring spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets over the temperature range 4–50 K at 9.25 and 36.4 GHz for different orientations of the
external magnetic field in relation to the crystallographic axes. The temperature dependence of the relaxation rate is described
by T
1
−1
=AT
n+b exp(−Δ/kT), where n varies from sample to sample, with n=1 for “perfect” samples (i.e., with the longest relaxation times). Here Δ is approximately 130 cm−1, which is the energy of the excited Kramers doublet of the neodymium ion closest to the ground state, and this makes it possible
to interpret the second term in T
1
−1
as the contribution of two-stage relaxation proceeding through the intermediate level Δ. A strong field dependence of these
processes has been discovered: when the frequency was increased fourfold, the relaxation rate increased by a factor of 10.
The effect is a specific manifestation of the degeneracy of the excited level, breaking of the symmetry of the crystalline
field due to lattice defects, and the prevalence of deformations of a certain type in the spin-lattice interaction.
Zh. éksp. Teor. Fiz. 111, 332–343 (January 1997) 相似文献
5.
M. N. Kiselev A. S. Mishchenko 《Journal of Experimental and Theoretical Physics》1998,86(5):1008-1019
A self-consistent microscopic theory of the relaxation of the crystal-field levels of an impurity ion in a state with an integer
valence implanted in a normal metal is devised. A microscopic approach based on the Coqblin-Schrieffer-Cooper approach, rather
than the formal model of the sf exchange interaction, makes it possible to take into account the specific details of both the crystal-field states of the
impurity ion and the electronic band spectrum of the metal. A new method for the soft spectroscopy of electronic states based
on measurements of the temperature dependence of the width ΓMM′(T) of transitions between the crystal-field states |M〉 of a paramagnetic ion implanted in the compound being studied is proposed. To make specific use of this method in neutron
and optical spectroscopy, a classification of the types of temperature dependence of the natural relaxation width γ
M
(T) of the levels is devised, and procedures for possible experimental methods are proposed. A nonzero value of the natural
relaxation width γ
G
(T) of the crystal-field ground state | G〉 of an impurity ion at zero temperature is obtained within the proposed self-consistent
model, but is beyond the scope of perturbation theory. It is shown that the widely accepted estimate of the characteristic
temperature of Kondo systems T*=Γ
G(T=0)/2 from the quasielastic scattering width at zero temperature Γ
G
(T=0)/2 is incorrect in the case of strong relaxation in a system with soft crystal fields. The proposed model is applied to
the quantitative analysis of the relaxation of the crystal-field levels of paramagnetic Pr3+ ions implanted in CeAl3 and LaAl3. The results of the calculations are in quantitative agreement with the experimental data.
Zh. éksp. Teor. Fiz. 113, 1843–1865 (May 1998) 相似文献
6.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
7.
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
8.
V. D. Blank V. M. Levin V. M. Prokhorov S. G. Buga G. A. Dubitskii N. R. Serebryanaya 《Journal of Experimental and Theoretical Physics》1998,87(4):741-746
The elastic properties of C60 fullerite samples synthesized under pressure P=13.0 GPa at high temperatures were investigated using acoustic microscopy. The velocities of longitudinal (c
L=17–26 km/s) and transverse (c
T=7.2–9.6 km/s) elastic waves in the samples were measured. It was established that the longitudinal sound velocity of ultrahard
fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard samples is higher than that of
diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substantial
Poisson ratio indicate that the structure of the ultrahard fullerites is fundamentally different from that of diamond.
Zh. éksp. Teor. Fiz. 114, 1365–1374 (October 1998) 相似文献
9.
Krishnamurthy V. V. Watanabe I. Nagamine K. Kitagawa J. Ishikawa M. Komatsubara T. 《Hyperfine Interactions》2001,136(3-8):385-389
Magnetic and quadrupolar ordering phenomena in a Ce3Pd20Ge6 single crystal have been investigated by muon spin rotation/relaxation (μ+SR) spectroscopy. We have observed spontaneous precession of muons in zero-field below T
N
=0.7 K in the antiferromagnetic state. The precession frequency follows the power law: ν(T)=ν(0)(1−T/T
N
)
n
. The exponent n=0.43(2) is close to the mean-field value of 0.5. The muon longitudinal spin relaxation rate 1/T
1 is found to be nearly independent of temperature in the range of 0.3 to 2 K, i.e., across either T
N
or T
Q
=1.2 K, the quadrupolar ordering temperature. Two likely mechanisms for the temperature independent behavior of 1/T
1 are suggested.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
10.
A. V. Anan’ev Yu. I. Zhdanov A. P. Gerashchenko K. N. Mikhalev S. V. Verkhovskii E. Yu. Medvedev K. A. Okulova N. I. Chebotaev V. N. Goshchitskii 《JETP Letters》1998,67(3):182-188
The spin-spin relaxation rate 63
T
2
−1
of 63Cu nuclei in CuO2 layers is measured in the normal and superconducting states of the compound YBa2Cu3O6.9 (T
c
onset
=94 K) subjected to radiation-induced disordering by a fast-neutron flux Φ to T
c
onset
=68 K (Φ=7×1018 cm−2) and T
c
onset
<4 K (Φ=12×1018 cm−2). It is found that as the structural disorder increases, the contribution of the indirect spin-spin interaction 63
T
2G
−1
, which is related to the value of the spin susceptibility at the boundary of the Brillouin zone of the copper planes χs(q={π/a; π/a}), decreases slightly at the transition to the superconducting state for the initial sample and remains unchanged for the
weakly disordered sample. This behavior of the short-wavelength contribution to the spin susceptibility attests to the stability
of the x
2−y
2 symmetry of the energy gap against structural disorder, in accordance with proposed theoretical models of Cooper pairing
for high-T
c cuprates.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 172–177 (10 February 1998) 相似文献
11.
Summary The thermal conductivity of YBa2Cu3O7−δ high-T
c superconductor is analysed self-consistently on both normal and superconducting states on the base of the Bardeen-Rickayzen-Tewordt
extended theory to take into account the effects of magnetic field and superconducting fluctuations. It is shown that experimental
data are in a quantitative agreement with theory even if the number and variation intervals of adjustable parameters are substantially
reduced in comparison with previous works. Phonon relaxation rates due to different mechanisms of phonon scattering as well
as the parameters of electron-phonon interaction are estimated. It is shown that thermal conductivity in YBa2Cu3O7−δ is consistent with the BCS model with intermediate electron-phonon coupling λ=1–3 the phonon-electron and electron-phonon
relaxation times near critical temperature are evaluated to be 10−10s and 10−12s, respectively. 相似文献
12.
L. Schimmele A. Seeger W. Staiger W. Templ C. Baines A. Fritzsche M. Hampele D. Herlach K. Maier J. Major 《Hyperfine Interactions》1991,64(1-4):671-677
The longitudinalμ
+-spin relaxation rate has been measured on a high-purity spherical α-iron single crystal at temperaturesT down to 20 mK and in applied magnetic fieldsB
appl parallel to 〈111〉 up to 3 T. Only above 1 K can the data be satisfactorily described by one rate constantГ. At 1 T≤B
appl≤2 T and 50 mK≤T≤300 mK, oscillations (“wiggles”) were in addition superimposed on the longitudinal relaxation. A qualitative understanding
of the measurements may be achieved in terms of the increasing influence of internal stresses onμ
+ diffusion as the temperature is lowered. 相似文献
13.
G. G. Fedoruk 《Journal of Experimental and Theoretical Physics》1997,84(4):665-668
This paper reports the results of an experimental study of the decay of transient NMR nutations in a two-level spin system
with homogeneous line broadening. The NMR nutation signals in glycerin were studied for 10⩽ω
1
T
2⩽150, where ω
1=γH
1, with γ the gyromagnetic ratio and H
1 the amplitude of the magnetic component of the radio-frequency field, and T
2 is the transverse relaxation time. It is found that in a high-power field (ω
1
T
2≫1) the nutation decay rate is independent of ω
1 and is quantitatively described by Bloch’s model. The data is compared with the data on non-Bloch (ω
1-dependent) EPR-nutation decay in quartz (R. Boscaino, F. M. Gelardi, and J. P. Corb, Phys. Rev. B 48, 7077 (1993)).
Zh. éksp. Teor. Fiz. 111, 1207–1213 (April 1997) 相似文献
14.
T. Zemčík 《Hyperfine Interactions》1990,55(1-4):1099-1102
A systematic increase of the average hyperfine magnetic induction at57Fe measured at room temperature during interrupted isothermal annealing was found to be inherent to the irreversible relaxation
processes in the Fe−B based soft magnetic alloys at moderately elevated temperatures. Assuming superimposed asymptotic exponential
field vs. time dependences. several processes can be distinguished, their relaxation times determined and from the Arrhenius-like
log τ vs. 1/T plots average activation enthalpies estimated. Results on the Fe70Co10B20 and Fe85−x
Co
x
B15 (x=17, 19 and 21 at. % Co) amorphous ribbons between 100 and 200°C are compared and discussed in terms of possible stress relief,
free volume annihilation and short range ordering mechanisms. 相似文献
15.
The four-dimensional Ising model is simulated on the Creutz cellular automaton using finite-size lattices with linear dimension
4≤L≤8. The exponents in the finite-size scaling relations for the order parameter and the magnetic susceptibility at the finite-lattice
critical temperature are computed to be β=0.49(7), β=0.49(5), β=0.50(1) and γ=1.04(4), γ=1.03(4), γ=1.02(4) for 7, 14, and 21 independent simulations, respectively. As the number of independent simulations increases, the
obtained results are consistent with the renormalization group predictions of β=0.5 and γ=1. The values for the critical temperature of the infinite lattice T
c
(∞)=6.6788(65), T
c
(∞)=6.6798(69), T
c
(∞)=6.6802(70) are obtained from the straight-line fit of the magnetic susceptibility maxima using 4≤L≤8 for 7, 14, and 21 independent simulations, respectively. As the number of independent simulations increases, the obtained
results are in very good agreement with the series expansion results of T
c
(∞)=6.6817(15), T
c
(∞)=6.6802(2), the dynamic Monte Carlo result of T
c
(∞)=6.6803(1), the cluster Monte Carlo result of T
c
(∞)=6.680(1) and the Monte Carlo using Metropolis and Wolff-cluster algorithm result of T
c
(∞)=6.6802632±5×10−5. 相似文献
16.
S. V. Demishev A. V. Semeno N. E. Sluchanko N. A. Samarin A. N. Vasil’ev L. I. Leonyuk 《Journal of Experimental and Theoretical Physics》1997,85(5):943-948
Resonant absorption of microwaves in CuGeO3 single crystals in a frequency band of 40 to 120 GHz, in magnetic field B⩽15 T, at temperatures ranging between 0.5 and 300 K, and in the configuration B∥a has been investigated. Several absorption lines (S
0, S
a, and S
b) whose parameters strongly depend on temperature have been detected close to ESR. The temperature dependence of the total
absorption in the main line S
0 with the Landé g-factor g
0=2.154 at temperatures above the spin-Peierls transition temperature is in good agreement with Bonner and Fisher’s theoretical
prediction for a one-dimensional Heisenberg spin chain. In addition to the main resonance, a resonance of smaller amplitude,
S
a, with the g-factor g
a=2.72 has been detected at temperatures ranging down to a characteristic temperature T≃1 K, below which the amplitude of this feature drops to zero. A radical restructuring of the magnetoabsorption spectrum occurs
at the temperature of the spin-Peierls transition T
SP≈14 K. At T<12 K new features emerge in the spectrum, namely, a broad absorption line overlapping with the narrow lines S
0 and S
a, and a line S
b with g
b=1.83, which is not detected at temperatures above T
SP. An analysis of amplitudes and total absorption of ESR lines as functions of temperature has shown that the temperature range
below 1 K is anomalous, which may be caused by an additional ordering in the CuGeO3 magnetic subsystem at low temperatures.
Zh. éksp. Teor. Fiz. 112, 1727–1738 (November 1997) 相似文献
17.
The behavior of the thermal conductivity k(T) of bulk faceted fullerite C60 crystals is investigated at temperatures T=8–220 K. The samples are prepared by the gas-transport method from pure C60, containing less than 0.01% impurities. It is found that as the temperature decreases, the thermal conductivity of the crystal
increases, reaches a maximum at T=15–20 K, and drops by a factor of ∼2, proportional to the change in the specific heat, on cooling to 8 K. The effective phonon
mean free path λ
p, estimated from the thermal conductivity and known from the published values of the specific heat of fullerite, is comparable
to the lattice constant of the crystal λ
p∼d=1.4 nm at temperatures T>200 K and reaches values λp∼50d at T<15 K, i.e., the maximum phonon ranges are limited by scattering on defects in the volume of the sample in the simple cubic
phase. In the range T=25−75 K the observed temperature dependence k(T) can be described by the expression k(T)∼exp(Θ/bT), characteristic for the behavior of the thermal conductivity of perfect nonconducting crystals at temperatures below the
Debye temperature Θ (Θ=80 K in fullerite), where umklapp phonon-phonon scattering processes predominate in the volume of the
sample.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 651–656 (25 April 1997) 相似文献
18.
D. G. Sannikov 《Journal of Experimental and Theoretical Physics》1997,84(2):293-299
An explanation is given for the narrow peak in the temperature dependence of the component α
32 of the magnetoelectric effect tensor near the transition at T=T
c to the m′m2′ phase observed in the boracites. A phenomenological approach is used which is based on the symmetry of the cubic phase
of the crystals. The change in the sign of α
23 and α
32 observed in some of the boracites as the temperature is lowered is attributed to the low value of T
c.
Zh. éksp. Teor. Fiz. 111, 536–546 (February 1997) 相似文献
19.
T. V. Panchenko 《Physics of the Solid State》1997,39(7):1085-1090
Anomalies of the dielectric properties of undoped and aluminum-and gallium-doped crystals of Bi12SiO20 are investigated in the frequency and temperature range ν=102–108 Hz and T=300–800 K. They are shown to be due to Debye relaxation processes and determined by the relaxor parameters. The mechanism
of electron thermal polarization is discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 1223–1229 (July 1997) 相似文献
20.
A. A. Verevkin N. G. Ptitsina K. V. Smirnov G. N. Gol’tsman E. M. Gershenzon K. S. Ingvesson 《JETP Letters》1996,64(5):404-409
The temperature dependence of the energy relaxation time τe (T) of a two-dimensional electron gas at an AlGaAs/GaAs heterointerface is measured under quasiequilibrium conditions in the
region of the transition from scattering by acoustic phonons to scattering with the participation of optical phonons. The
temperature interval of constant τe, where scattering by the deformation potential predominates, is determined. In the preceding, low-temperature region, where
piezoacoustic and deformation-potential-induced scattering processes coexist, τ e decreases slowly with increasing temperature. Optical phonons start to participate in the scattering processes at T∼25 K (the characteristic phonon lifetime was equal to τLOτ4.5 ps). The energy losses calculated from the τe data in a model with an effective nonequilibrium electron temperature agree with the published data obtained under strong
heating conditions.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 371–375 (10 September 1996) 相似文献