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1.
Dislocation motion at various velocities in Na23Cl single crystals was studied using the spin-locking technique. The resulting spin-lattice relaxation time in the rotating frame, T1?, is strongly dependent on the plastic deformation rate ?e, but not on the plastic strain ?. The experimental results are in accord with a theoretical expression for T1? based on the relaxation model of Rowland and Fradin for atomic diffusion.  相似文献   

2.
The sensitivity of the19F spin-lattice relaxation dispersion, T1,(ω), to motional disorder in crystalline superionic conductors of the type La1?xSrxF3?x (x = 0; 0.03) is shown. T1 times are measured in the frequency range from 90 kHz to 370 MHz using standard techniques in combination with field-cycling. The relaxation dispersion shows qualitative differences from the standard Bloembergen-Purcell-Pound behavior. At low frequencies a relaxation model using a distribution of correlation times for diffusing ions is found to be consistent with the experimental results. At frequencies higher than 50 MHz another process of the Debye type which is not induced by ionic hopping dominates the relaxation.  相似文献   

3.
The 1H NMR line-width and spin-lattice relaxation time T1 of TSCC single crystals were studied. Variations in the temperature dependence of the spin-lattice relaxation time were observed near 65 and 130 K, indicating drastic alterations of the spin dynamics at the phase transition temperatures. The changes in the temperature dependence of T1 near 65 and 130 K correspond to phase transitions of the crystal. The anomalous decrease in T1 around 130 K is due to the critical slowing down of the soft mode. The abrupt change in relaxation time at 65 K is associated with a structural phase transition. The proton spin-lattice relaxation time of this crystal also has a minimum value in the vicinity of 185 K, which is governed by the reorientation of the CH3 groups of the sarcosine molecules. From this result, we conclude that the two phase transitions at 65 and 130 K can be discerned from abrupt variations in the 1H NMR relaxation behavior, and that 1H nuclei play important roles in the phase transitions of the TSCC single crystal.  相似文献   

4.
The temperature evolution of the proton spin-lattice relaxation time T1 in p-terphenyl and in p-quaterphenyl around their order-disorder phase transition has been measured. In both cases pretransitional collective fluctuations destroy the high temperature Arrhenius behaviour of the relaxation rate corresponding to a single reorientational jump motion. The spin-lattice relaxation times present then a drastic decrease until the transition temperature (T0 = 193 K in p-terphenyl, T0 = 238 K in p-quaterphenyl). This decrease is associated to the critical slowing down of fluctuations. In the low temperature phase the ordering phenomena lead to a sharp drop of the spin-lattice relaxation rate.  相似文献   

5.
A simple classical model for nuclear spin-lattice relaxation due to solitons in XY one-dimensional magnetic chains in an external magnetic field is discussed. The results show that one should expect opposite behavior for the H/T dependence of T-11 for the ferromagnetic and the antiferromagnetic case.  相似文献   

6.
The spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets (YAG) and for Yb3+ ions in CaF2 in the low-temperature range have been measured. For the first system the temperature dependence of the relaxation rate is determined to a great extent by the method of sample preparation. For samples grow by the method of the horizontally oriented crystallization the dependence is described asT 1 ?1 =AT n ,n ? 4.7, which is an evidence of an influence of local structure disordering on the relaxation. The temperature dependence of the relaxation rate in CaF2:Yb is also “anomalous”:T 1 ?1 =AT 3.3. The results are compared with the previous data on the relaxation in similar systems, and with other cases of observation of “anomalous” temperature dependences. Different manifestations of the local crystal defects in spin-lattice relaxation are discussed.  相似文献   

7.
The35C1-NQR frequency (VQ), nuclear quadrupole spin-lattice relaxation time (T1Q),1H-NMR second moment (M 2), nuclear magnetic spin-lattice relaxation time (T 1) and spin-lattice relaxation time in rotating frame (T 1p ) were measured for polycrystalline clofibric acid (drug) as a function of temperature. Hindered rotation of two dynamically inequivalent methyl groups and the phenyl ring was detected, the relevant activation energies were determined. The rotations are discussed in detail.  相似文献   

8.
The spin-lattice relaxation rates of 1H and 39K nuclei in KHSeO4 crystals were studied in the temperature range 160-400 K. The spin-lattice relaxation recovery of 1H nucleus in this crystal can be represented with a single exponential function, and the relaxation T1−1 curve of 1H can be represented with the Bloembergen-Purcell-Pound (BPP) function. The relaxation process of 39K with dominant quadrupole relaxation can be described by a linear combination of two exponential functions. T1−1 for the 39K nucleus was found to have a very strong temperature dependence, T1−1=βT7. Rapid variations in relaxation rates are associated with critical fluctuations in the electronic spin system. The T7 temperature dependence of the Raman relaxation rate is shown here to be due to phonon-magnon coupling.  相似文献   

9.
Nuclear magnetic resonance of cobalt metal was investigated in the paramagnetic and ferromagnetic states and in the critical region below Tc. The Knight shift and spin lattice relaxation times were measured in the paramagnetic phase in the solid and liquid states from 1578 K to 1825 K. The resonant frequency, spin-lattice and spin-spin relaxation times were measured in the ferromagnetic phase from room temperature to 1385 K. The main part of (T1T)-1 results from fluctuating orbital moments in both phases except near Tc where this process forms the background for critical spin relaxation. The critical exponents for T-11 and for the magnetization in the ferromagnetic state were found to be n' = 0.96 ± 0.07 and β = 0.308 ± 0.012, respectively.  相似文献   

10.
With an original modulation technique, the Gd3+ electron spin-lattice relaxation has been investigated in normal and superconducting states of YBa2Cu3O6+x (123) and YBa2Cu4O8 (124) compounds doped with 1% Gd. In the 123 sample withx = 0.9T c = 90 K), theT 1 behavior within 50 <T< 200 K reveals the [1 ? tanh2(Δ/2kT)]/T dependence typical of a spin gap opening with Δ ≈ 240 K. Below 50 K, the exponential slowing down ofT 1 is limited by the Korringa-like behaviorT 1 T = const); the same Korringa-like law is found in the 123 sample withx = 0.59 (T c = 56 K) within the total 4.2–200 K temperature range. This is interpreted in terms of microscopic separation of the normal and superconducting phases allowing for the electron spin cross-relaxation between them. In the 124 sample (T c = 82 K), the Gd3+ relaxation rate below 60 K is found to obey a power lawT n with an exponentn ≈ 3. Such a behavior (previously reported for nuclear spin relaxation) is indicative of the d-wave superconducting pairing. Additional paramagnetic centers characterized by relatively slow spin-lattice relaxation are found in both 123 and 124 systems. A well-pronounced change in theT 1 temperature dependence atTT* ≈ 180–200 K is observed for these slowly relaxing centers as well as for the conventional, fast-relaxing Gd3+ ions, suggesting microscopic phase separation and a change in the relaxation mechanism due to electronic crossover related with the opening of the spin gap. This hypothesis is supported by some “180 K anomalies” previously reported by other authors.  相似文献   

11.
The magnetic properties of an s?=?1/2 Heisenberg triangular antiferromagnet V15 have been studied by proton nuclear magnetic resonance (NMR) at very low temperature down to 100 mK using a He3-He4 dilution refrigerator. In total spin S T?=?3/2 ground state above 2.7 Tesla, proton spin-lattice relaxation rate (1/T1) shows thermally activated behavior as a function of temperature. On the other hand, a temperature independent behavior of 1/T1 at very low temperatures is observed in frustrated S T?=?1/2 ground state below 2.7 Tesla. Possible origins for the peculiar behavior of 1/T1 will be discussed in terms of magnetic fluctuations due to spin frustration.  相似文献   

12.
The 133Cs spin-lattice relaxation time in a CsHSO4 single crystal was measured in the temperature range from 300 to 450 K. The changes in the 133Cs spin-lattice relaxation rate near Tc1 (=333 K) and Tc2 (=415 K) correspond to phase transitions in the crystal. The small change in the spin-lattice relaxation time across the phase transition from II to III is due to the fact that during the phase transition, the crystal lattice does not change very much; thus, this transition is a second-order phase transition. The abrupt change of T1 around Tc2 (II-I phase transition) is due to a structural phase transition from the monoclinic to the tetragonal phase; this transition is a first-order transition. The temperature dependences of the relaxation rates in phases I, II, and III are indicative of a single-phonon process and can be represented by T1−1=A+BT. In addition, from the stress-strain hysteresis loop and the 133Cs nuclear magnetic resonance, we know that the CsHSO4 crystal has ferroelastic characteristics in phases II and III.  相似文献   

13.
The molecular motion contrast parameter for NMR imaging of solids and quasi-solids based on the spin-lattice relaxation (T leff) in multiple-pulse experiments is discussed. For Ostroff-Waugh multiple-pulse sequence theT leff contrast parameter is evaluated in slow and fast molecular motion regime and compared with spin-lattice relaxation in the rotating frame contrast parameter. It is shown thatT leff is offering a good molecular motion contrast in NMR imaging of polymer systems. The radio-frequency pulse scheme forT leff-imaging using magic-echo phase-encoding procedure for recording spatial distribution in solids is introduced. A method forT leff-weighted imaging using gradient spin-echo valid for weak dipolar solids is also discussed. The one-dimensional protonT leff image using Ostroff-Waugh pulse sequence in combination with frequency-encoding imaging procedure is presented for a phantom of poly(ethyleneoxide) and poly(methylmethacrylate). The distribution of mechanical stresses in a acrylate film on glass is investigated by protonT leff-imaging. A proton spin-density image weighted byT leff, for a mixture of two elastomers with different crosslink density is also shown.  相似文献   

14.
The temperature dependence of the proton spin-lattice relaxation time has been measured at 51, 70 and 300 MHz by different pulse sequences. Besides a strongly frequency dependent background relaxation rate, a frequency independent critical relaxation rate could be resolved particularly in a broad temperature interval above Tc. The temperature dependence of the critical relaxation rate could not be represented by a power law with a single exponent. Rather it most favourably could be fitted by a logarithmic law. The results are discussed with respect to the phase transition mechanism of squaric acid.  相似文献   

15.
The electron spin-lattice and spin-spin phase relaxation measurements of Cu2+ ions in various crystals are reviewed and discussed. Examples of the Debye temperature determination from a wide temperature range measurements of the spin-lattice relaxation time T1 are shown. An influence of the Jahn-Teller dynamics on T1 is presented. The phase relaxation described by the phase memory time TM is affected by temperature due to the spin packet width modulation by molecular motions. The TM is anisotropic in crystals and can be different for different hyperfine lines of an EPR spectrum.  相似文献   

16.
The temperature dependence of the spin-lattice relaxation time T 1 and the 7Li NMR spectra of the Li0.7Nb3Se4 intercalation compound with one-dimensional channel structure have been studied. It is found that the temperature dependence of T 1 exhibits two relaxation minima, and the quadrupole splitting in the Li NMR spectra shows an anomalous temperature behavior. The inference is drawn that the observed effects are associated with the high-rate diffusive motion of lithium ions along one-dimensional channels and the interchannel transitions.  相似文献   

17.
The diffusion of hydrogen in palladium (HPd = 0.73) has been investigated from 170 to 300K by measurements of the proton spin-lattice relaxation time in the rotating frame, T1?. In contrast to previous T1 measurements, a single activation energy of 0.225 eV is obtained, in agreement with the high-temperature T1 data and with internal friction experiments at about 120K.  相似文献   

18.
The temperature dependence of the proton spin-lattice relaxation times T1 and T1? were measured in some partially deuterated ammonium compounds; ammonium perchlorate and ammonium dichromate. The extremely large minimum values of T1? (2 ~ 3 sec) were found to be independent of the concentration of deuterons. These minima of T1? were attributed to the random modulation of the dipolar interaction between the protons and 17O (0.037%) of low abundance. The activation energy Ea of the reorientation of ClO4 and CrO3 were determined to be 6.2 and 10.7 kcal mol-1, respectively.  相似文献   

19.
Measurements of B11 nuclear spin-lattice relaxation as a function of temperature in the itinerant antiferromagnet CrB2 are reported. T-11 shows a divergent behavior near TN and it approaches a constant value well above TN. The results are compared with the different theoretical predictions of Moriya and Ueda obtained either from the RPA or from the renormalized spin fluctuation approach.  相似文献   

20.
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