Proton NMR study of α-MnH0.06

Proton nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates for the solid solution α-MnH_0.06 have been measured over the temperature range 11-297 K and the resonance frequency range 20-90 MHz. A considerable shift and broadening of the proton NMR line and a sharp peak of the spin-lattice relaxation rate are observed near 130 K. These effects are attributed to the onset of antiferromagnetic ordering below the Néel temperature T_N≈130 K. The proton NMR line does not disappear in the antiferromagnetic phase; this suggests a small magnitude of the local magnetic fields at H-sites in α-MnH_0.06. The spin-lattice relaxation rate in the paramagnetic phase is dominated by the effects of spin fluctuations.     

Proton magnetic resonance study of the low-temperature phase transition in a LiNH4SO4 single crystal

The proton NMR line width and spin-lattice relaxation times for LiNH₄SO₄ single crystal were studied at low temperature range of 6 and 280 K. The changes in the proton relaxation behavior near the phase transition temperature indicates a change in the state of internal motion at the transition. The molecular motions obtained by the spin-lattice relaxation processes were found to be determined by molecular reorientation of the NH₄ ions in phases III, IV, and V. We also confirmed that the phase transitions occur at 26 and 133 K.     

NMR study of the phase transition in HfV2H3.9

The ⁵¹V Knight shift and quadrupole interaction, the spin-lattice relaxation time for ⁵¹V and ¹H, and the magnetic susceptibility in HfV₂H_3.9 and HfV₂H_3.2 are studied between 20 and 320 K. The sharp changes in magnetic susceptibility and NMR lineshape indicating a phase transition are found for HfV₂H_3.9 near 296 K. In the low-temperature phase the hydrogen atoms are ordered and at least two inequivalent V sites exist. It is shown that the hydrogenation of HfV₂ leads to a considerable decrease in the density of electron states at the Fermi level.     

1H NMR study of the α phase of Mg2NiHx system

Hydrogen behavior in the α phase of Mg₂NiH_x system was studied by ¹H NMR. ¹H NMR spectra and spin-lattice relaxation times, T₁ and T_1ρ, of Mg₂NiH_0.22 were measured in the temperature range between 100 and 480 K. The drastic change in the linewidth is observed between 170 and 340 K, and ¹H rigid lattice is observed below 170 K, from which it is deduced that the hydrogen atoms are randomly distributed in α-Mg₂NiH_x. The relaxation mechanism for t₁ is the paramagnetic one, while the T_1ρ value is determined partially by hydrogen diffusion. The hydrogen diffusion rate has been determined from the linewidth and the T_1ρ value. The paramagnetic relaxations observed in T₁ and T_1ρ have been discussed relating to the hydrogen diffusion.     

F NMR and EPR study of fluorinated buckminsterfullerene C60F58

Solid state ¹⁹F NMR in the temperature range from 96 to 366 K and room temperature EPR studies of fluorinated buckminsterfullerene C₆₀F₅₈ have been carried out. The temperature dependence of the line width and the spin-lattice relaxation time show hindered molecular motion with the activation energy of ΔE_a=1.9 kcal/mol. Neither phase transition nor random rotation of C₆₀F₅₈ have been obtained. The spin-lattice relaxation rate is strongly affected by the presence of paramagnetic centers, namely, dangling C-C bonds yielding localized unpaired electrons. Such broken bonds are caused by C-C bond rupture in a cage-opened structure of hyperfluorinated species.     

NMR spectral densities and two dimensional diffusion in TiS2(NH3)1.0 and TaS2(NH3)x

NMR measurements of proton spin-lattice relaxation times T₁ and T_1? in the layered intercalation compounds TiS₂(NH₃)_1.0 and TaS₂(NH₃)_x (x = 0.8, 0.9, 1.0) are reported as functions of frequency and temperature (100 K – 300 K). These observations probe the spectral density of magnetic fluctuations due to motions of the intercalated molecules at frequencies accessible to the T₁ (4–90 MHz) and T_1? (1–100 kHz) measurements. Since the average molecular hopping time (τ) can be changed by varying temperature, different regions of the spectral density can be examined. For T > 200 K, both T^?1₁ and T^?1_1? vary logarithmically with frequency, reflecting the two dimensional character of the molecular diffusion. The temperature dependence of T₁ suggests that a more accurate picture of the short time dynamics is required. No dependence of relaxation rate on vacancy concentration is found.     

Proton NMR study of the central peak in ferroelastic KH3 (SeO3)2

Measurements of the temperature and the magnetic field dependence of the proton spin-lattice relaxation time T₁ in KH₃ (SeO₃)₂ show the presence of a dynamic narrow central peak in the local proton fluctuation spectrum the width of which is less than 0.1 MHz.     

Co2+ spin-lattice relaxation narrowing of 19F NMR in KCoF3

The temperature dependence of the ¹⁹F NMR linewidth ΔH in KCoF₃ has been measured over the entire paramagnetic solid state region. The dramatic decrease in the hyperfine-broadened, exchange narrowed ΔH that occurs above 200 K is interpreted as arising from fast Co²⁺ single-ion, spin-lattice relaxation. A model theory of the temperature dependence of ΔH is given which incorporates the interplay of exchange and spin lattice relaxation effects on the decay of the spin autocorrelation function.     

Étude par rmn de la localisation et des mouvements des protons dans les hydrures MgH2 et Mg2NiH4

Wide line and pulsed NMR studies are reported for MgH₂; and Mg₂NiH₄ hydrides at 79 and 30 MHz in the temperature range between 100 and 500 K. Line shape data confirm a rutile type structure for MgH₂, and lead to the evaluation that 97% of the hydrogen is present in this phase, the remainder being in solid solution MgH_x, (x<0.04).Mg₂NiH₄ shows a Gaussian line, whose peak-to-peak width decreases from 6.16 to 4.28 G in the range 320–365 K. From 365 to 480 K the spectrum shows a second, narrower, line (0.85 G), implying that approximately 7% of the protons have migrated from their initial position to energetically less stable sites. The thermal behaviour of the T₁ and T₂ relaxation times shows a dramatic variation in the 320–370 K temperature range in connection with the change of the proton localization. Relaxation mechanisms can be attributed mainly to conduction electron-nucleus interactions. With rising temperature, diffusion mechanisms are also involved. A diffusion activation energy of about 0.35 eV has been determined, with a diffusion coefficient 3.45 × 10^?8 < D < 4.6 × 10^?8 cm²/s.     

离子导体LiCl(Al2O3)的核磁共振研究

本文报道了含分散第二相粒子的离子导体LiCl(或LiI)中⁷Li核磁共振的观测结果,测量了⁷Li核磁共振吸收谱线的线宽和自旋-晶格弛豫时间(T₁)。实验发现,在LiCl(Al₂O₃)中,⁷Li的核磁共振吸收谱线上叠加了一小峰,且随第二相粒子的类型、含量和温度而变化。⁷Li核磁共振信号的信噪比显著提高,自旋-晶格弛豫时间变短,且也随第二相粒子的类型、含量和温度而变化。结果表明,离子电导率的提高和附加小峰的出现都是由第二相粒子引起的,从而提出:靠近第二相粒子的LiCl界面附近的空间电荷区中高的离子传导是离子电导率提高和附加小峰出现的可能机理。 关键词：     

Proton NMR in CeNiInH0.53 down to liquid helium temperature

The NMR probe and the matching network has been designed for the¹H NMR study in CeNiInH_0.53 down to liquid helium temperature using Bruker MSL 100 spectrometer. NMR line-shape measurement shows the absence of any signature of proton pairing in CeNiInH_0.53 down to 3.86 K, as it was observed for high hydrogen concentration. The measurement of the spin-lattice relaxation time in the temperature range 300–20K reveals that the relaxation rate is mainly governed by the Korringa-type relaxation mechanism.     

A 1H NMR study of the effects of Ni additions on the behavior of hydrogen in β-vanadium hydride

The behavior of hydrogen in the hydrides of vanadium metal containing small amounts of nickel was studied by ¹H NMR spectroscopy. FT spectra and spin-spin and spin-lattice relaxation times for VH_0.77, V_0.95Ni_0.05H_0.73, and V_0.90Ni_0.10H_0.65 were measured at temperatures between 77 and 400 K. On the addition of nickel the number of hydrogen atoms on O₂₂ sites decreases and the superstructure of hydrogen is altered. Different effects of nickel on hydrogen diffusion are observed above and below about 200 K, and, therefore, the mechanism of hydrogen diffusion is assumed to change at this temperature.     

A study of molecular motion and Raman processes in K3H(SO4)2 and KHSO4 single crystals by observation of H and K spin-lattice relaxation

The spin-lattice relaxation rates for ¹H and ³⁹K nuclei in K₃H(SO₄)₂ and KHSO₄ single crystals, which are potential candidate materials for use in fuel cells, were determined as a function of temperature. The spin-lattice relaxation recovery of ¹H can be represented for both crystals with a single exponential function, but cannot be represented by the Bloembergen-Purcell-Pound (BPP) function, so is not related to HSO₄ motion. The recovery traces of ³⁹K, which predominantly undergoes quadrupole relaxation, can be represented by a linear combination of two exponential functions. The temperature dependences of the relaxation rates for ³⁹K can be described with a simple power law T₁⁻¹=αT². The spin-lattice relaxation rates for the ³⁹K nucleus in K₃H(SO₄)₂ and KHSO₄ crystals are in accordance with a Raman process dominated by a phonon mechanism.     

Al NMR studies of NpPd5Al2

We present ²⁷Al NMR studies for a single crystal of the Np-based superconductor NpPd₅Al₂. We have observed a five-line ²⁷Al NMR spectrum with a center line and four satellite lines separated by first-order nuclear quadrupole splittings. The Knight shift clearly drops below T_c. The temperature dependence of the ²⁷Al nuclear spin-lattice relaxation rate shows no coherence peak below T_c, indicating that NpPd₅Al₂ is an unconventional superconductor with an anisotropic gap. The analysis of the present NMR data provides evidence for strong-coupling d-wave superconductivity in NpPd₅Al₂.     

H NMR study of the phase transitions of trissarcosine calcium chloride single crystals at low temperature

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.     

Nuclear magnetic resonance study of the relaxation mechanisms of the Be, Al, and Si nuclei in Cr-doped Be3Al2Si6O18 crystals

The variations with temperature of the relaxation mechanisms of the ⁹Be, ²⁷Al, and ²⁹Si nuclei in emerald (Be₃Al₂Si₆O₁₈:Cr³⁺) single crystals were investigated by using a pulse NMR spectrometer. The values of the spin-lattice relaxation rates for the three nuclei are different, and these differences are attributed to the differences between their Larmor frequencies and their local nuclear environments. The relaxation rates of the ⁹Be and ²⁷Al nuclei undergo no abrupt changes within the temperature range 180-400 K, which indicates that there are no phase transitions within this temperature range. The spin-lattice relaxation rates of ⁹Be and ²⁷Al were found to be proportional to temperature. Therefore, the nuclear spin-lattice relaxation processes of these two nuclei proceed via single-phonon processes.     

The NMR study of the mixed compound (CH3NH3)2Cu(Cl0.1Br0.9)4

The mixed compound (CH₃NH₃)₂Cu(Cl_0.1Br_0.9)₄ which has random bonds of ferromagnetic and antiferromagnetic interactions has been investigated by the pulsed NMR of ¹H, ^63,65Cu and ^79,81Br. The temperature dependence of the line width of ¹H showed the existence of the magnetic phase transition at 15 K in the applied field of 4 kOe. The moments of Cu²⁺ have been shown to lie within the c-plane and have some randomness from the field dependence of the NMR spectrum and the spin-echo decay time of the copper and the bromine nuclei.     

Hydrogen absorption in CeFe2 and ThFe3

The effect of hydrogen absorption on the magnetic properties of CeFe₂ and ThFe₃ was studied by magnetization measurements and by the ⁵⁷Fe Mössbauer effect. In both cases an increase in the transition metal moment is observed. In CeFe₂ the long range periodicity of the crystal lattice is lost whereas in ThFe₃ a structural change occurs. Surprisingly, the magnetic anomaly observed in ThFe₃ around 250 K is still present in the hydride.     

Specific heat of EuIn2P2 at high magnetic fields

We have carried out specific heat measurements on EuIn₂P₂ at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear λ-type anomaly due to a magnetic transition at , indicating that the magnetic transition is of second-order. The λ-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu²⁺ magnetic moments align ferromagnetically perpendicular to the c-axis below T_C. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu²⁺ multiplet by internal magnetic fields.     

Proton NMR relaxation study of the CsHSO4 solid acid system

At 141 °C the solid acid CsHSO₄ is known to undergo transition to a superprotonic phase that is characterized by dramatic (several-order-of-magnitude) increases in hydrogen ion conductivity. Proton NMR spin-spin relaxation time T₂ measurements reported here for CsHSO₄ also reveal substantial increases (factors of 20-30) in the vicinity of the transition temperature. In the temperature range just below the transition (70-136 °C), T₂ increases by a factor of order 10 relative to the rigid-lattice regime, suggesting motional narrowing of the NMR resonance line. In the regime of motional narrowing, the activation energy barrier to diffusion is 0.40 eV, as determined from the present T₂ results. NMR spin-lattice relaxation T₁ measurements also show behavior consistent with transition to a regime of rapid hydrogen motion. In particular, proton T₁'s decrease with temperature (from 80 to 120 °C), and then drop sharply near the transition temperature. Above the transition temperature, T₁ exhibits a minimum in which the correlation time is found to be ∼2 ns.