Separation of the impurity and lattice components of the spin-lattice relaxation of Al27 nuclei in corundum crystals under magnetic saturation conditions

The impurity and lattice contributions to the spin-lattice relaxation of Al²⁷ nuclei in nominally pure and lightly chromium-doped corundum (Al₂O₃) crystals are separated experimentally under the conditions of additional stationary resonance magnetic saturation of a pulsed NMR signal. The relaxation time T _i ^lat due to the lattice mechanism of the spin-phonon interaction is determined. Fiz. Tverd. Tela (St. Petersburg) 39, 1041–1043 (June 1997)     

Measurement of the spin-lattice relaxation time in the NQR of light nuclei

This work proposed a method for increasing the signal/noise ratio in NQR by preliminary magnetization of the sample in a constant magnetic field B₀ and its subsequent adiabatic demagnetization. The proposed method for the measurement of spin-lattice relaxation times is verified experimentally with a number of compounds. The results agree well with published data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 88–91, July, 1987.     

Temperature dependence of nuclear spin-lattice relaxation in the heavy-fermion superconducting state

Some features of the experimental data on nuclear spin relaxation time T₁ in the heavy-fermion superconducting state can be explained by taking into account the effect of the electron Zeeman energy. It is found that at intermediate temperatures the usual quasiparticle spin-flip scattering dominates, while at very low temperatures a new process, pair creation (annihilation), dominates and gives T^-1₁ ∝ T.     

Temperature dependence of the spin-lattice relaxation time in local triplet-excited states of a doped C60 fullerene crystal

The temperature dependence of the spin-lattice relaxation time of triplet-excited impurity centers of a C₆₀ fullerene crystal is investigated within the framework of the spin-phonon coupling mechanism which arises as a result of the admixture of rotational to translational motions of the molecules due to acoustic lattice vibrations. General expressions are obtained for the transition probabilities for the direct single-phonon and Raman two-phonon processes. The method of atom-atom potentials is used to carry out a concrete calculation of the spin-lattice relaxation time for an isotopic impurity in a C₆₀ crystal. Fiz. Tverd. Tela (St. Petersburg) 39, 1699–1702 (September 1997)     

Study of activation parameters and NMR spin-lattice relaxation time in some substituted amines

The present communication reports the experimental values of NMR spin-lattice relaxation time (T₁) and dielectric relaxation time (τ) of piperidine, pyrrole, pyridine, diethylamine, triethylamine and pyrrolidine. The values of activation energy (ΔE_A) obtained using dielectric relaxation time, have been correlated with calculated values of ΔE_A obtained using Arrhenius equation of NMR relaxation time (T₁) for pyridine, diethylamine and pyrrole. Authors have also established a correlation between the experimental values of NMR spin-relaxation time (T₁) with its calculated values obtained using different equations of dielectric relaxation time (τ).     

Angular dependence of the Knight shift, electric field gradient, and spin-lattice relaxation time of 9Be NMR in beryllium metal

Angular dependences of ⁹Be NMR (±1/2) and (±1/2 ? ±3/20 transition frequencies are measured in a single-crystal beryllium metal plate in a field of 7.04T. The isotropic K _iso and anisotropic K _aniso components of the Knight shift are determined. The measured values of K _iso and T ₁ are considered in terms of the contact, polarization, and orbital contributions.     

Field dependence of spin-lattice relaxation in paramagnetic salts

The field dependence of the Raman SLR rate is determined for H₀ of the order of the local field. Both S-state and non S-state transition salts are investigated when (i)H_dip > H_exch and (ii) H_exch > H_dip. Measurements are obtained from the response of the longitudinal magnetization to an amplitude modulated microwave field. The observed dependences agree with Orbach-Huang calculations.     

Proton spin-lattice relaxation time of hydrated gelatin

In this work we obtain a model to describe the relaxativity of water molecules, adsorbed on macromolecules, as a function of the concentration. Excellent agreement with experimental data was obtained. The model allows us to estimate the adsorption energy of water molecules on different sites of the macromolecules.     

Temperature dependence of the relaxation time of the superconducting order parameter

We have measured the temperature dependences of the relaxation time of the superconducting order parameter and of the equilibrium energy gap close to the transition temperature in very clean films of aluminum. The results are only consistent with the temperature and energy gap dependence predicted by Schmid and Schön. We also show that the magnitude and mean free path dependence of the electron inelastic collision time is in good agreement with calculations.     

Temperature dependence of the order-parameter relaxation time of a superconducting indium film

We have measured the critical d.c. current of a superconducting indium bridge in the presence of a superimposed a.c. current for frequencies up to 400 MHz. The temperature dependent order parameter relaxation time has been determined from these experiments, yielding the value τ_E = 80 ps for the inelastic electron phonon scattering time.     

NMR study of one-dimensional ionic conductor with hollandite-type structure. II. Frequency dependence of spin-lattice relaxation time of 27Al

Frequency dependence of spin-lattice relaxation time T₁ of ²⁷Al in one-dimensional K⁺ ion conductor, K-Al-priderite, was measured at 45 K in the frequency range from 10.1 MHz to 55 MHz. It is found that T₁ is proportional to ω^1.49±0.05 and agrres well with the $\text{ω}{}^{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}$ dependence derived by the continuum diffusion model. The intrinsic activation energy is determined to be 0.058 eV by doubling the slope E_NMR=0.029 eV of the d(ln T₁)/dT curve in the low temperature region. The frequency dependence of T₁ in the high temperature region measured in the frequency range from 11.5 MHz to 20.8 MHz shows a tendency that the frequency dependence becomes smaller than the $\text{ω}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ dependence as temperature is raised above 450 K.     

Temperature and frequency dependence of the spin-lattice relaxation times of E′1 centers in neutron-irradiated quartz glass

Results are reported for measurements of the spin-lattice relaxation times of E′₁ centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm⁻¹. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation of irradiation centers in crystalline quartz and quartz glass. Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997)     

Effect of oxidation of cobalt-based nanowires on NMR spin-lattice relaxation

Nuclear spin-lattice relaxation measurements were performed on Co-based magnetic nanowires, in zero field and in 1 T applied field. A measurement method is developped that allows a confident interpretation of the experimental data. An enhanced relaxation due to a thermally activated phenomenon associated to oxidation is reported for the first time in the nuclear magnetic resonance of ferromagnetic systems.     

NMR relaxation in multipolar AMX systems under spin-locking conditions

A relaxation network has been calculated for multipolar AMX systems under application of a spin-locking RF field. Systems of this type are of interest in the study of proteins with fractional ²H enrichment. All possible auto- and cross-correlation terms involving dipolar, quadrupolar, and CSA interactions have been taken into account. The results show the presence of spectral densities at zero frequency for interactions associated with the locked nuclei, which are nonvanishing in the absence of fast motions. In addition, the application of a spin-locking field blocks certain cross-correlation interactions, thereby considerably simplifying the relaxation network.     

Mechanism of nuclear spin-lattice relaxation and its field dependence for ultraslow atomic motion

The contribution of ultraslow self-diffusion of polycrystalline benzene molecules to the spin-lattice relaxation of protons is studied as a function of effective magnetic field H ₂ in a doubly rotating frame (DRF). Proton relaxation time T _1ρρ is measured by direct recording of NMR in a rotating frame (RF). The effective fields have a “magic” orientation corresponding to angles arccos(1/√3) in the RF and π/2 in the DRF so that the secular part of the dipole-dipole interactions of protons is suppressed in two orders of perturbation theory, while the nonsecular part becomes predominant. It is found that the diffusion contribution of benzene molecules to proton relaxation time T _1ρρ is a linear function of the square of field H ₂ and exhibits all peculiarities typical of the model of strong collisions generalized to only fluctuating nonsecular dipole interactions in fields exceeding the local field. This means that the model can also be employed in the given conditions. It is shown that perfect agreement with such a dependence can also be obtained in the model of weak collisions if we take into account the concept of the locally effective quantization field, whose magnitude and direction are controlled by the vector sum of field H ₂, and the nonsecular local field perpendicular to it.     

Temperature dependence of the circular random walk relaxation time in nematic liquid crystal

Temperature dependence of the quasi-elastic neutron spectra were measured on an aligned and not aligned nematic material. The relaxation time and the activation energy were determined.     

Magnetic field dependence of spin-lattice relaxation enhancement using piperidinyl nitroxyl spin-labels

We examined the magnetic resonance properties of 12 paramagnetic piperidinyl nitroxyls in water and plasma solutions. Paramagnetic contributions to proton relaxation times were measured using 10.7 and 100 MHz spectrometers. Proton relaxation enhancement from nitroxyls increased with ascending molecular weight, in plasma solutions versus equimolar aqueous solutions, and with measurements at 10.7 MHz compared to 100 MHz. Relaxation rates were observed to approximately double at 10.7 MHz compared to 100 MHz and from water to plasma solutions. The data indicate that proton spin-lattice relaxation enhancement is magnetic field-dependent, and increases using nitroxyls of large molecular weight and with chemical substitutents that increase the microviscosity of solvent water molecules. The development of nitroxyls for diagnostic MRI will be aided by understanding these in vitro physical characteristics and trends.