Nuclear Magnetic Quadrupole Research Articles

Application of nuclear quadrupole resonance under 10 GPa class pressure at low temperature

The high pressure nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) are conventionally performed up to 3 GPa using piston cylinder cell. However, the NMR/NQR measurements beyond this pressure range are scarcely performed owing to the technical difficulty. Recently, we developed new high pressure NMR/NQR technique using cubic anvil apparatus with which highly hydrostatic pressure was obtained. Using the new method, the 63Cu-NQR signal of Cu2O was observed up to 7.2GPa in nearly hydrostatic condition with high sensitivity. It was noted that the appropriate choice of pressure-transmitting medium is important for accurate experiments.

Magnetic anomalies of hydrous cobaltate compoundNax(H3O)zCoO2⋅yH2Odetected by NMR and NQR measurements

In order to investigate the relationship between superconductivity and magnetism in bilayer-hydrate cobaltate ${\text{Na}}_{x}{({\text{H}}_{3}\text{O})}_{z}{\text{CoO}}_{2}\ensuremath{\cdot}y{\text{H}}_{2}\text{O}$ Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements were performed on three different samples, which demonstrate various ground states at low temperatures. The appearance of small internal fields is observed in the NQR spectra below approximately 6 K on one of the samples that possesses the largest $c$-axis length and the highest NQR frequency. The other two samples exhibit superconducting transition in zero magnetic field, while these two samples show different ground states in the magnetic fields greater than 5 T. The comparison of the NMR spectra of these two samples obtained in high magnetic fields reveals the appearance of static internal magnetic fields at the Co site below 4 K in the sample that possesses the intermediate $c$-axis length and the NQR frequency.

Lithium-doped (4,4) Boron nitride nanotube: Density functional theory study of N and B nuclear magnetic shielding and electric field gradient tensors

First principle values of nuclear magnetic shieldings and nuclear quadrupole coupling constants of B and N nuclei via density functional theory (DFT) were calculated for a hydrogen-capped (4,4) single-walled boron nitride nanotube (BNNT) (raw model) and a lithium-doped derivative of it (Li-doped model). The models were first fully relaxed and then the C Q and nuclear magnetic shielding tensor calculations were accomplished. Probing the results shows a heterogeneous electrostatic environment along the nanotube length with different layers. The disparity of results among this work and the other similar calculations is blatant .The computations were fully implemented by Gaussian 98 Software package.

B24N24 nanocages: a GIAO density functional theory study of 14N and 11B nuclear magnetic shielding and electric field gradient tensors

AbstractDensity functional theory (DFT) calculations were performed to determine boron-11 and nitrogen-14 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy parameters in the three most stable B 24 N 24 fullerenes for the first time. The considered samples were first allowed to relax entirely, and then the NMR and NQR calculations were performed on the geometrically optimized models. The calculations of the 11 B and 14 N nuclear magnetic shielding tensors and electric field gradient tensors employed the Gaussian 98 software implementation of the gauge-including atomic orbital (GIAO) method using the Becke3, Lee-Yang-Parr (B3LYP) DFT level and 6-311G** and 6-311++G** standard basis sets in each of the three optimized forms, and converted the results to experimentally measurable NMR parameters.The calculated NMR chemical shieldings of the three cages show significant differences, providing a way to identify these clusters. The evaluated NQR parameters of the 11 B and 14 N nuclei in the clusters are also reported and discussed.Graphical abstract[IMAGE]

Application of Nuclear Quadrupole Resonance with Mini Cubic Anvil Apparatus

A wide variety of experimental methods under high pressure are now applied to various materials. For nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) methods, high pressure measurements up to about 3.5GPa are performed conventionally because of the development of hybrid cylinder clamp cells. In this pressure range, we have examined the suitable pressure transmitting media, which can give more hydrostatic pressure to sample, by comparing the Cu-NQR spectral width of Cu2O and its pressure efficiency between room temperature and 4.2K. Further high pressures for the NMR/NQR methods can be achieved by an indenter-type clamp cell (up to about 5GPa), a modified Bridgman anvil cell (up to about 10GPa), and so on. However, these higher pressure measurements are not general at present stage because of their smaller sample space than that of the piston cylinder cell. Typically the diameter and the height of the sample space is ’ 1:7mm and h ’ 1:4mm for the indenter-type clamp cell and ’ 1:0mm and h ’ 1:0mm for the modified Bridgman anvil cell, while that for the piston cylinder cell is ’ 4:0mm and h ’ 20mm or larger. Moreover, it is quite difficult to obtain hydrostatic pressure above about 5GPa. This is because the pressure by the Bridgman anvil at higher pressures has a tendency of uniaxial stress to sample space. Cubic anvil apparatus has an advantage in this point since the cubic anvil apparatus can induce pressure nearly isotropically to sample space. It can also achieve high pressure up to about 20GPa. The line width of Cu-NQR of Cu2O is a good measure of pressure homogeneity since the pressure homogeneity inside pressure cell is strongly related to the broadening of NMR/NQR spectra. Hence, we performed Cu-NQR measurements of Cu2O up to about 7.5GPa with mini cubic anvil apparatus in order to obtain more hydrostatic pressure under 10GPa-class high pressure. Note that the sample space itself is comparable to that of the indenter-type cell and about four times larger than that of the modified Bridgman anvil cell; ’ 2:0mm diameter and h ’ 1:0mm height. This larger sample enables us to obtain strong enough intensity even at room temperature. To the best of our knowledge, this is the first report on the NMR/NQR measurement with the use of the cubic anvil apparatus. The Cu-NQR measurements of Cu2O were performed using a phase-coherent pulsed NQR spectrometer in the resonance frequency range 26–29MHz. We used Cu2O powder (99.9%) and glycerin mixed with the ratio of 20 : 1. Inside the sample coil, this mixture was set up. We consider that a small amount of the glycerin does not behave as pressure transmitting medium. We performed the NQR measurements at room temperature (about 300K). The obtained spin echo data were Fourier transformed to NQR spectra. Below about 3GPa, the line shape at a pressure was obtained at an excitation resonance frequency because the line shape was narrow enough to detect by measuring NQR pulse width. We used mini cubic anvil apparatus (Fig. 1) which is recently developed by Takeshita et al. We use nonmagnetic WC anvil top at present stage, but we can change other nonmagnetic and insulating anvil tops. Its overall volume including of cryostat is about 30 times smaller than that of conventional cubic anvil apparatus for low temperature measurements. Furthermore, the weight of its guide block is approximately 3 kg, which is about 7 times lighter than that of conventional one. However, its sample space is the same as that of the conventional one. The present maximum pressure of this apparatus is about 10GPa with the use of MgO gasket, but we used pyrophyllite gasket in this study, with which the maximum pressure of the apparatus is about 7.5GPa, in order to ensure reproducibility. Single-layer coil wound about 20 turns was used in our measurements ( 1⁄4 1:5mm, h 1⁄4 0:7mm). We used a 1 : 1 mixture of Fluorinert 70 and 77 (Fluorinert). In our previous Cu-NQR measurements of Cu2O with hybrid piston cylinder cell, the pressure homogeneity using Fluorinert medium was the worst among the available pressure media above 1GPa. We also used Fluorinert with the modified Bridgman anvil cell where the large pressure inhomogeneity exists. In this study, we examine the pressure homogeneity of the mini cubic anvil apparatus and compare the pressure homogeneity with various apparatus using the same pressure transmitting medium. We may expect the drastic improvement of the homogeneity with the cubic anvil apparatus even using the Fluorinert. Fig. 1. (Color online) A mini cubic apparatus and its guide block on the palm.

Ferromagnetic Quantum Critical Fluctuations and Anomalous Coexistence of Ferromagnetism and Superconductivity in UCoGe Revealed by Co-NMR and NQR Studies

Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies were performed in the recently discovered UCoGe, in which the ferromagnetic and superconducting (SC) transitions were reported to occur at $T_{\rm Curie} \sim 3$ K and $T_S \sim 0.8$ K (N. T. Huy {\it et al.}, Phys. Rev. Lett. {\bf 99} (2007) 067006), in order to investigate the coexistence of ferromagnetism and superconductivity as well as the normal-state and SC properties from a microscopic point of view. From the nuclear spin-lattice relaxation rate $1/T_1$ and Knight-shift measurements, we confirmed that ferromagnetic fluctuations which possess a quantum critical character are present above $T_{\rm Curie}$ and the occurrence of ferromagnetic transition at 2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal state show that UCoGe is an itinerant ferromagnet similar to ZrZn$_2$ and YCo$_2$. The onset SC transition was identified at $T_S \sim 0.7$ K, below which $1/T_1$ of 30 % of the volume fraction starts to decrease due to the opening of the SC gap. This component of $1/T_1$, which follows a $T^3$ dependence in the temperature range of $0.3 - 0.1$ K, coexists with the magnetic components of $1/T_1$ showing a $\sqrt{T}$ dependence below $T_S$. From the NQR measurements in the SC state, we suggest that the self-induced vortex state is realized in UCoGe.

Pressure induces interdigitation differently in DPPC and DPPG

The phase behaviours of chain-perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62) and chain-perdeuterated dipalmitoylphosphatidylglycerol (DPPG-d62) bilayers were compared using 2H nuclear magnetic resonance spectroscopy and quadrupole echo decay measurements over pressures ranging from ambient to 196 MPa and temperatures ranging from 60 to -25 degrees C. At ambient pressure, the phase behaviours of DPPC-d62 and DPPG-d62 were nearly identical. At 196 MPa, their behaviours were also very similar and both lipids appeared to pass from an interdigitated gel phase at high temperature, through a non-interdigitated gel phase at intermediate temperature, to a chain-immobilized ordered phase at low temperature. At 85 MPa, the behaviour of DPPC-d62 was similar to its ambient pressure behaviour with no evidence of interdigitation. For DPPG-d62, however, the behaviour at 85 MPa was similar to its higher pressure behaviour and spectra characteristic of an interdigitated gel phase were observed. Pressure-temperature phase diagrams for both lipids were compared. While the minimum pressure for DPPC-d62 interdigitation is about 150 MPa, DPPG-d62 was observed to interdigitate at pressures as low as 60 MPa. Given the similarity of their phase behaviours at both higher and lower pressures, this difference reflects the extent to which bilayer phase behaviour depends on the balance between interactions in the headgroup and hydrocarbon regions of the bilayer.

Hyperfine magnetic anomaly in isotopic pairs 151, 152Eu and 152, 153Eu

High-resolution laser spectroscopy measurements of optical hyperfine splitting on the 151, 152, 153Eu isotopes were performed on the atomic transition 4f76s28S7/2 → 4f76s6p6P5/2 at λ ≈ 564.58 nm. Values of the nuclear magnetic dipole and electric quadrupole moments are obtained from the measured hyperfine splitting and the magnetic hyperfine anomalies in the isotope pairs 151, 152Eu and 152, 153Eu are deduced. The absolute values of the hyperfine anomaly in both cases are unusually large: 5 (1)%. The possible sources causing these anomalies are discussed.

Anisotropic spin fluctuations and anomalies of nuclear quadrupole interactions in the itinerant antiferromagnetNpCoGa5:Co59NMR andGa69,71NMR/NQR studies

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments have been performed on a single crystal of tetragonal $\mathrm{Np}\mathrm{Co}{\mathrm{Ga}}_{5}$, an itinerant antiferromagnet with a N\'eel temperature ${T}_{N}=47\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The antiferromagnetic phase is inverted to a field-induced ferromagnetic (FIF) phase with an applied field $({H}_{0})$ above ${H}_{m}$ $(T\ensuremath{\rightarrow}0)$ $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ oriented along the $c$ axis. NMR spectra have been measured above and below ${T}_{N}$ with ${H}_{0}\ensuremath{\Vert}c$ and $a$ axes and have been assigned to $^{69,71}\mathrm{Ga}$ nuclei on two crystallographically inequivalent $1c$ and $4i$ sites and to $^{59}\mathrm{Co}$ nuclei on the $1b$ site. Using second-order perturbation calculations, Knight shift $(K)$, electric field gradient (EFG), frequency $({\ensuremath{\nu}}_{\mathrm{Q}})$, and asymmetry parameter $(\ensuremath{\eta})$ of the EFG are deduced for each site. These parameters for the $^{69}\mathrm{Ga}(1c)$ and $^{69,71}\mathrm{Ga}(4i)$ sites are confirmed by NQR measurements in zero field. The Knight shifts obtained in the paramagnetic (PM) state obey a Curie-Weiss law, which scales with the bulk susceptibility $(\ensuremath{\chi})$. Hyperfine tensors for each site are deduced from $K\ensuremath{-}\ensuremath{\chi}$ plots with temperature as an implicit parameter. Antiferromagnetic NMR spectra in zero field were also observed, finding an internal field of $\ensuremath{\sim}20\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ at the $\mathrm{Ga}(4i)$ site at the lowest temperature. The ordered moment can be estimated from this to be $0.81\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}∕\mathrm{Np}$. The nuclear quadrupolar parameters (${\ensuremath{\nu}}_{\mathrm{Q}}$ and $\ensuremath{\eta}$) are found to exhibit an anomaly just below ${T}_{N}$ in the FIF phase. ${T}_{1}$ and ${T}_{2}$ have been measured for each site. For ${H}_{0}\ensuremath{\Vert}c$, ${T}_{1}\ensuremath{\sim}\text{constant}$ behavior suggests localized $5f$ character for $T>100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and itinerant $(1∕{T}_{1}\ensuremath{\propto}T)$ behavior for ${T}_{N}<T<\ensuremath{\sim}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $\mathrm{Np}\mathrm{Co}{\mathrm{Ga}}_{5}$. ${T}_{2}$ measurements in the case of ${H}_{0}\ensuremath{\Vert}c$ clearly define a phase crossover between PM and FIF phases. A sharp anisotropy for spin fluctuations in $\mathrm{Np}\mathrm{Co}{\mathrm{Ga}}_{5}$ has also been demonstrated.

Nuclear Magnetic Resonance Chemical Shifts and Quadrupole Couplings for Different Hydrogen-Bonding Cases Occurring in Liquid Water: A Computational Study

Nuclear magnetic resonance (NMR) parameters are determined theoretically for the oxygen and hydrogen/deuterium nuclei of differently hydrogen-bonded water molecules in liquid water at 300 K. The parameters are the chemical shift, the shielding anisotropy, the asymmetry parameter of shielding, the nuclear quadrupole coupling constant, and the asymmetry parameter of the nuclear quadrupole coupling. We sample instantaneous configurations from a Car-Parrinello molecular dynamics simulation and feed nuclear coordinates into a quantum chemical program for the calculation of NMR parameters using density-functional theory with the three-parameter hybrid exchange-correlation (B3LYP) functional. In the subsequent analysis, molecules are divided into groups according to the number of hydrogen bonds they possess, and the full average NMR tensors are calculated separately for each group. The classification of the hydrogen-bonding cases is performed using a simple distance-based criterion. The analysis reveals in detail how the NMR tensors evolve as the environment changes gradually from gas to liquid upon increasing the number of hydrogen bonds to the molecule of interest. Liquid-state distributions of the instantaneous values of the NMR properties show a wide range of values for each hydrogen-bonding species with significant overlap between the different cases. Our study shows how local changes in the environment, along with classical thermal averaging, affect the NMR parameters in liquid water. For example, a broken or alternatively extra hydrogen bond induces major changes in the NMR tensors, and the effect is more pronounced for hydrogen or deuterium than for oxygen. The data sheds light on the usefulness of NMR experiments in investigating the local coordination of liquid water.

Reply to “Comment on ‘Localized behavior near the Zn impurity inYBa2Cu4O8as measured by nuclear quadrupole resonance’ ”

Julien et al. have commented on two of our publications claiming that we have made erroneous interpretations of the nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) data. Specifically, they believe that their model of an extended staggered moment about a Zn impurity is the only interpretation of the data [Julien et al., Phys. Rev Lett. 84, 3422 (2000)]. Not only does their claim ignore models presented by other authors, we show that the model of Julien et al. [Phys. Rev Lett. 84, 3422 (2000)] does not consistently reproduce all of the NMR data.

Molecular dynamics studies of vitreous boron oxide

Several structural investigations using diffraction techniques, Raman spectroscopy, nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) have supported the idea that the structure of vitreous B2O3 (v-B2O3) is built up predominantly by planar B3O6 rings. Most Molecular Dynamics (MD) studies can be better understood by a continuous random network of BO3. In this work the structure of v-B2O3 has been investigated by MD simulations. The magnitude of the differences in model density samples is studied as a function of the ratio of structural units (B3O6 versus BO3). The difference in this ratio in generated structures was obtained by two cooling cycles: Cycle I is simulating a quenched structure while the Cycle II intents to reproduce a slowly cooled structure. It is shown that for structures containing several hundred atoms MD simulations give a considerable variation for the ratio of building units. The computed density for the obtained structures could not reach experimental density values for either of the cooling cycles. The number of boron atoms in boroxol rings is higher in the structures generated with slow cooling but is less than the predicted one of 80%.

Time-dependence of nuclear magnetic resonance quadrupole interactions for polymers under shear

We consider the problem of performing NMR spectroscopy under conditions of flow, a central issue in Rheo-NMR. By way of example, the effects of rotational motion on the deuterium NMR spectrum are considered for Couette cell experiments involving deformation of polymers under shearing conditions. The polymer was modelled as a power law fluid and for each streamline, the spin Hamiltonian evolved to allow for flow reorientation. The gap-integral spectra are compared with the ‘ideal’ spectra for a polymer under shear, but without reorientation. It is found that flow does affect the shape of the deuterium spectra, as well as slightly perturbing the splittings.

Nuclear magnetic shielding and quadrupole coupling tensors in liquid water: a combined molecular dynamics simulation and quantum chemical study.

Nuclear magnetic resonance (NMR) shielding tensors for the oxygen and hydrogen nuclei, as well as nuclear quadrupole coupling tensors for the oxygen and deuterium nuclei of water in the liquid and gaseous state, are calculated using Hartree-Fock and density functional theory methods, for snapshots sampled from Car-Parrinello molecular dynamics trajectories. Clusters representing local liquid structures and instantaneous configurations of a single molecule representing low-density gas are fed into a quantum chemical program for the calculation of the NMR tensors. The average isotropic and anisotropic tensorial properties of 400 samples in both states, averaged using a common Eckart coordinate frame, are calculated from the data. We report results for the gas-to-liquid chemical shifts of (17)O and (1)H nuclei, as well as the corresponding change in the nuclear quadrupole couplings of (17)O and (2)H. Full thermally averaged shielding and quadrupole coupling tensors are reported for the gaseous and liquid-state water, for the first time in the case of liquid. Electron correlation effects, the difference of classical vs quantum mechanical rovibrational averaging, and different methods of averaging anisotropic properties are discussed.

Confirmation of the Existence of Modulation Wave Motion in Incommensurate Rb2ZnCl4 by Hahn Echo and 2D NMR

87Rb Hahn echo nuclear magnetic resonance (NMR) and 35Cl Hahn echo nuclear quadrupole resonance (NQR) measurements were performed at 293 - 302 K in the incommensurate (I) phase of Rb2ZnCl4. The existence of a Hahn echo decay that is shorter than the true T2 and one that has an exponential dependence on the cube of the echo time indicates the presence of slow motions. The diffusion coefficient D can be obtained from the rate of decay of the Hahn echo. Similar values for D were obtained from the two different measurements, indicating that both the Rb and the Cl atoms are experiencing the same motional mechanism. This mechanism must be due to simultaneous motions of each and can not be due to individual motions of only one type of atom. Further confirmation of the presence of modulation wave motion was obtained from 87Rb two-dimensional (2D) exchange-difference NMR measurements.

Superconductivity and magnetic fluctuations in Cd(2))Re(2)O(7) via Cd nuclear magnetic resonance and re nuclear quadrupole resonance.

We report Cd nuclear magnetic resonance (NMR) and Re nuclear quadrupole resonance (NQR) studies on Cd(2)Re(2)O(7), the first superconductor among pyrochlore oxides (T(c) approximately 1 K). The Re NQR spectrum at zero magnetic field below 100 K rules out any magnetic or charge order. The spin-lattice relaxation rate below T(c) exhibits a pronounced coherence peak and follows the weak-coupling BCS theory with nearly isotropic energy gap. The results of Cd NMR point to a moderate ferromagnetic enhancement at high temperatures followed by a rapid decrease of the density of states below the structural transition temperature of 200 K.

Clues Obtained from the Oxygen Isotope Effect on NMR/NQR Parameters Observed in YBa 2 Cu 4 O 8

Nuclear magnetic and nuclear quadrupole resonance (NMR, NQR) techniques have a precision allowing one to determine rather small isotope effects. Well-defined oxygen stoichiometry and negligible oxygen diffusion makes YBa2Cu4O8 an ideal compound for studies of small isotope effects that require experimental results not hampered by reproducibility problems. We report on high-precision measurements of the temperature dependence of plane-63,65Cu NMR/NQR parameters such as Knight shift, spin–lattice relaxation rate R = 1/T 1, NQR line frequency νQ and NQR linewidth δνQ, as well as 89Y Knight shift, performed in normal and superconducting 16O and 18O exchanged YBa2Cu4O8.

Cu NMR and NQR Studies of the Doped Spin-Peierls System CuGe1-xSixO3

Nuclear magnetic and nuclear quadrupole resonance (NMR and NQR) of Cu have been measured in the doped spin-Peierls system CuGe 1 - x Si 2 O 3 . We find evidence that the staggered polarization of Cu 2 + spins due to doping is not induced near the Si doping center. It occurs in-between Si atoms, wiping out a part of Cu nuclei far from Si while leaving those near Si observable as NQR/NMR satellites. Local susceptibility measurements via the NMR shifts suggest preformation of singlet dimers near Si above the spin-Peierls transition temperature. These observations may be understood by effective interruption of a linear chain of Cu by Si, and the formation of strong bonds on the edges of a segment which is favored by an inherent spin-phonon coupling.

Electromagnetic moments of the beta-emitting nucleus 16N.

The nuclear magnetic dipole moment mu and electric quadrupole moment Q of the beta-emitting 16N(Ipi = 2(-), T(1/2) = 7.13 s) nucleus have been determined for the first time by detecting its beta-NMR in a MgO crystal and beta-NQR (nuclear quadrupole resonance) in a TiO (2) crystal to be /mu/ = (1.9859+/-0.0011) mu(N) and /Q/ = (17.9+/-1.7) mb, respectively. Although the prediction of mu given by the Hartree-Fock calculation agrees well with the experiment, an abnormally small effective charge for neutrons is required to account for the experimental Q.

Magnetic field dependence of the superconducting fluctuation contribution to NMR-NQR relaxation

The dependence of the Maki-Thompson and of the density of states (DOS) depletion contributions from superconducting fluctuations to nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) relaxation is derived in the framework of the diagrammatic theory, applied to layered three-dimensional (3-D) high-Tc superconductors. The regularization procedure devised for the conductivity (A. I. Buzdin, A. A. Varlamov: Phys. Rev. B58, 14195, 1998) is used in order to avoid the divergence of the DOS term. The theoretical results are discussed in the light of NMR-NQR measurements in YBCO and compared with the recent theory (M. Eschrig et al.: Phys. Rev. B59, 12095, 1999), on the basis of the assumption of a purely 2-D spectrum of fluctuations.