Showing papers on "Nuclear quadrupole resonance published in 2005"

Anisotropic Superconducting Gap in Transuranium Superconductor PuRhGa5: Ga NQR Study on a Single Crystal

Abstract: 69,71 Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa 5 with T c ≃9 K. We have observed a 69 Ga NQR line at ∼29.15 MHz, and assigned it to the 4 i Ga site using the NMR results. The 69 Ga NQR spin–lattice relaxation rate 1/ T 1 shows no coherence peak just below T c , but obeys T 3 behavior below T c . This result strongly suggests that PuRhGa 5 is an unconventional superconductor having an anisotropic superconducting gap. The gap amplitude 2Δ 0 ( T →0)≃5 k B T c and the residual density of states N res ( T =0)/ N 0 ( T = T c )≃0.25 have been determined assuming a simple polar function of the form Δ(θ,φ)=Δ 0 cos θ, where θ and φ are angular parameters on the Fermi surface.

Magnetic Correlation of NaxCoO2 and Successive Phase Transitions of Na0:5CoO2 —NMR and Neutron Diffraction Studies—

Abstract: Data taken by various methods including NMR/NQR and neutron scattering are presented for Na x CoO 2 , particularly Na 0.5 CoO 2 . Attention has also been paid to the x dependence of the electronic nature of this system. The pseudo-gap-like behavior observed in the region of x < x c ∼0.6 is emphasized. For samples with x ≤0.6, signals from two kinds of Co sites with different quadrupole frequencies ν Q of ∼4.1 and ∼2.8 MHz were observed, and the former ν Q , which is nearly equal to that of the superconducting system Na 0.3 CoO 2 · y H 2 O, becomes dominant with decreasing x to 0.3. For Na 0.5 CoO 2 , the Co sites with the larger ν Q have larger magnetic moments. They align antiferromagnetically at T c1 ∼87 K with their direction within the plane, while the Co sites with the smaller ν Q have smaller moments. They align in the direction parallel to the c axis. The ordered moments at the two distinct sites exhibit the same T -dependence, indicating that the existence of these sites is not due to macroscopic ...

Potential of nuclear quadrupole resonance in pharmaceutical analysis

Abstract: Nuclear quadrupole resonance is a radio frequency (rf) spectroscopic technique, closely related to NMR, which can be used to detect signals from solids containing nuclei with spin quantum number >1/2. It is nondestructive, highly specific and noninvasive, requires no static magnetic field, and as such is currently used in the detection of explosives and narcotics. Recent technological advances in pulsed NQR methods have shortened detection times, eliminated spurious signals, and enhanced the sensitivity of detection of 14N frequencies, which lie in the low rf range of 0.4−6 MHz, encouraging a wider range of “real world” applications. This Perspective highlights some of the advantages of NQR, the applications in which it could be used, such as the quantification of pharmaceuticals and the identification of polymorphs. Other roles could include detection, analysis, and quality control of pharmaceuticals at all stages of manufacture. Finally, recent advances which enhance even further the sensitivity of dete...

Weak Magnetic Order in Bilayered-Hydrate NaxCoO2·yH2O Structure Probed by Co Nuclear Quadrupole Resonance –Proposed Phase Diagram in Superconducting NaxCoO2·yH2O–

Abstract: A weak magnetic order was found in a nonsuperconducting bilayered-hydrate Na x CoO 2 · y H 2 O sample by Co nuclear quadrupole resonance (NQR) measurement. The nuclear spin–lattice relaxation rate divided by temperature 1/ T 1 T shows a prominent peak at 5.5 K, below which a Co NQR peak splits due to an internal field at the Co site. From the analyses of the Co NQR spectrum at 1.5 K, the internal field is evaluated to be ∼300 Oe and found to be in the a b -plane. The magnitude of the internal field suggests that the ordered moment is as small as ∼0.015 µ B using the hyperfine coupling constant reported previously. It is shown that the NQR frequency ν Q correlates with magnetic fluctuations from measurements of NQR spectra and 1/ T 1 T in various samples. The higher-ν Q sample has stronger magnetic fluctuations. A possible phase diagram for Na x CoO 2 · y H 2 O is depicted using T c and ν Q , in which the crystal distortion along the c -axis of the tilted CoO 2 octahedron is considered to be a physical par...

Frequency-selective detection of nuclear quadrupole resonance signals

Abstract: Nuclear quadrupole resonance (NQR) offers an unequivocal method of detecting and identifying both hidden explosives, such as land mines, and a variety of narcotics. Unfortunately, the practical use of NQR is restricted by a low signal-to-noise ratio (SNR), and means to improve the SNR are vital to enable a rapid, reliable, and convenient system. In this paper, we introduce a frequency-selective approximate maximum-likelihood (FSAML) detector, operating on a subset of the available frequencies, making it robust to the typically present narrow-band interference. The method exploits the inherent temperature dependency of the NQR frequencies as a way to enhance the SNR. Numerical evaluations, using both simulated and real NQR data, indicate a significant gain in probability of accurate detection as compared to a current state-of-the-art approach.

Investigation of the crystal structure and the structural and magnetic properties of SrCu2(PO4)2.

Abstract: SrCu2(PO4)2 was prepared by the solid-state method at 1153 K. Its structure was solved by direct methods in the space group Pccn (No. 56) with Z = 8 from synchrotron X-ray powder diffraction data measured at room temperature. Structure parameters were then refined by the Rietveld method to obtain the lattice parameters, a = 7.94217(8) A, b = 15.36918(14) A, and c = 10.37036(10) A. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1...Cu2 = 3.256 A. The magnetic properties of SrCu2(PO4)2 were investigated by magnetic susceptibility, magnetization up to 65 T, Cu nuclear quadrupole resonance (NQR), electron-spin resonance, and specific heat measurements. With spin-dimer analysis, it was shown that the two strongest spin-exchange interactions between Cu sites result from the Cu1-O...O-Cu2 and Cu2-O...O-Cu2 super-superexchange paths with Cu1...Cu2 = 5.861 A and Cu2...Cu2 = 5.251 A, and the superexchange associated with the structural dimer Cu1Cu2O8 is negligible. The magnetic susceptibility data were analyzed in terms of a linear four-spin cluster model, Cu1-Cu2-Cu2-Cu1 with -2J(1)/kB = 82.4 K for Cu1-Cu2 and -2J(2)/k(B) = 59 K for Cu2-Cu2. A spin gap deduced from this model (Delta/kB = 63 K) is in agreement with that obtained from the Cu NQR data (Delta/kB = 65 K). A one-half magnetization plateau was observed between approximately 50 and 63 T at 1.3 K. Specific heat data show that SrCu2(PO4)2 does not undergo a long-range magnetic ordering down to 0.45 K. SrCu2(PO4)2 melts incongruently at 1189 K. We also report its vibrational properties studied with Raman spectroscopy.

Novel Phase Transition Near the Quantum Critical Point in the Filled-Skutterudite Compound CeOs4Sb12: An Sb-NQR Study

Abstract: We report on a novel phase transition at T = 0.9 K in the Ce-based filled-skutterudite compound CeOs 4 Sb 12 via measurements of the nuclear-spin lattice relaxation rate 1/ T 1 and nuclear quadrupo...

Ferromagnetic and Triplet-Pairing Instabilities Controlled by Trigonal Distortion of CoO6 Octahedra in NaxCoO2·yH2O

Abstract: In the recently discovered Co-oxide superconductor Na x CoO 2 · y H 2 O, the edge-shared CoO 6 octahedra are trigonally contracted along the c -axis in the CoO 2 -plane. We study how this CoO 6 distortion affects the magnetic properties and superconductivity in this compound by analyzing the multiorbital Hubbard model using the fluctuation-exchange approximation. It is shown that through generating the trigonal crystal field, the distortion pushes the Co e ′ g bands up and consequently gives rise to the hole-pocket Fermi surfaces, which have been predicted in the band calculations. As the distortion increases, the hole pockets are enlarged and the ferromagnetic fluctuation as well as the pairing instability increases, which is in good agreement with recent NQR results.

Anomalous temperature dependence of nuclear quadrupole interactions in strongly hydrogen-bonded systems from first principles.

Abstract: We present an analysis of the effect of finite temperatures on the deuteron nuclear quadrupole coupling constants in a strongly hydrogen-bonded molecular crystal by means of first-principles Car-Parrinello molecular-dynamics simulations. Our findings agree well with experiments and provide a microscopic explanation of the anomalous increase of the quadrupole coupling in this class of systems. We show that a simple model based on the anharmonicity of the hydrogen bond potential fails to describe the temperature dependence of the couplings even qualitatively. Instead, the inclusion of fluctuations and disorder in terms of atomic motion of the surrounding molecules turns out to be important to obtain the correct magnitude of the temperature effect.

Use of two or more sensors to detect different nuclear quadrupole resonance signals of a target compound

Abstract: The use of two or more sensors tuned to at least two different nuclear quadrupole resonance frequencies of a target compound to detect the different nuclear quadrupole resonance signals greatly reduces the chance of misidentification, and thereby improves nuclear quadrupole resonance detection system performance.

Heavy fermion compound SmOs4Sb12 in vicinity of ferromagnetic critical point

Abstract: We report nuclear quadrupole resonance (NQR) measurement at ambient pressure and resistivity measurement under high pressure in the new heavy fermion (HF) compound SmOs 4 Sb 12 . The NQR spectrum and the nuclear spin–lattice relaxation rate (1/ T 1 ) clearly demonstrate the bulk nature of ferromagnetic ordering below T C ∼2 K. The temperature dependence of 1/ T 1 exhibits the characteristic behaviors of a Kondo lattice. The application of pressure decreases Kondo temperature and stabilizes the magnetic ordering, which is the same tendency as that found in some Yb-based compounds. The obtained phase diagram indicates SmOs 4 Sb 12 to be in the vicinity of its ferromagnetic critical point.

Methods and apparatus for scanning a band of frequencies using an array of high temperature superconductor sensors

Abstract: The methods of the invention for scanning a band of frequencies using a nuclear quadrupole resonance detection system with an array of high temperature superconductor sensors to detect nuclear quadrupole resonance signals improve the nuclear quadrupole resonance detection system performance.

Decoupling high temperature superconductor sensor arrays in nuclear quadrupole resonance detection systems

Abstract: The decoupling of an array of two or more closely spaced high temperature superconductor sensors (1, 2) can be accomplished by introducing a capacitive decoupling circuit.

Scanning a band of frequencies using an array of high temperature superconductor sensors tuned to the same frequency

Abstract: The methods of the invention for scanning a band of frequencies using a nuclear quadrupole resonance detection system with an array of high temperature superconductor sensors to detect nuclear quadrupole resonance signals improve the nuclear quadrupole resonance detection system performance.

Cooperative phenomenon of ferromagnetism and unconventional superconductivity in UGe2: A 73Ge-NQR study under pressure

Abstract: We report on a cooperative phenomenon of ferromagnetism and unconventional superconductivity (SC) in UGe 2 through the measurements of 73 Ge nuclear-quadrupole-resonance (NQR) under pressure ( P )

Cu-spin dynamics at zigzag chain of superconducting and nonsuperconducting Pr247 compounds

Abstract: We present Cu nuclear quadrupole resonance (NQR) results for both superconducting Pr 2 Ba 4 Cu 7 O 14.5 (Pr247_S) and nonsuperconducting Pr 2 Ba 4 Cu 7 O 15 (Pr247_NS). We found that: (1) Below T c = 18 K, the 1/ T 1 T of the double chains in Pr247_S is appreciably smaller than that of Pr247_NS. On the other hand, the planar-site signals of Pr247_S disappear below 285 K, indicating the transferring into magnetically ordered state. To our knowledge, this is the first experimental evidence that the superconductivity of Pr247_S is driven and realized at the double chains, while the CuO 2 planes remain magnetically ordered. (2) For Pr247_NS, the temperature dependence of 1/ T 1 and 1/ T 2 at the double chains showed a pronounced peak at around 110 K and 50 K, respectively, which is similar to the reported behavior for Pr124 compound. In contrast, for Pr247_S, no anomalies are observed in 1/ T 1 or 1/ T 2 . This suggests that, above T c , the double chains of Pr247_S should be in the normal metallic state, unlike the case of Pr247_NS or Pr124.

Sb-NQR Probe for Multipole Degree of Freedom in the First Pr-Based Heavy-Fermion Superconductor PrOs4Sb12

Abstract: We report 121,123 Sb nuclear quadrupole resonance (NQR) measurements in the filled-skutterudite superconductor PrOs 4 Sb 12 in the temperature range of 0.05–30 K. The electric field gradients (EFG)...

The weakly bound He-HCCCN complex: high-resolution microwave spectra and intermolecular potential-energy surface.

Abstract: Rotational spectra of the weakly bound He-HCCCN and He-DCCCN van der Waals complexes were observed using a pulsed-nozzle Fourier-transform microwave spectrometer in the 7-26-GHz frequency region. Nuclear quadrupole hyperfine structures due to the 14N and D nuclei (both with nuclear-spin quantum number I = 1) were resolved and assigned. Both strong a and weaker b-type transitions were observed and the assigned transitions were used to fit the parameters of a distortable asymmetric rotor model. The dimers are floppy, near T-shaped complexes. Three intermolecular potential-energy surfaces were calculated using the coupled-cluster method with single and double excitations and noniterative inclusion of triple excitations. Bound-state rotational energy levels supported by these surfaces were determined. The quality of the potential-energy surfaces was assessed by comparing the experimental and calculated transition frequencies and also the corresponding spectroscopic parameters. Simple scaling of the surfaces improved both the transition frequencies and spectroscopic constants. Five other recently reported surfaces [O. Akin-Ojo, R. Bukowski, and K. Szalewicz, J. Chem. Phys. 119, 8379 (2003)], calculated using a variety of methods, and their agreement with spectroscopic properties of He-HCCCN are discussed.

Structure-activity study of thiazides by magnetic resonance methods (NQR, NMR, EPR) and DFT calculations.

Abstract: The paper presents a comprehensive analysis of the relationship between the electronic structure of thiazides and their biological activity. The compounds of interest were studied in solid state by the resonance methods nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) and quantum chemistry (ab inito and DFT) methods. Detailed parallel analysis of the spectroscopic parameters such as quadrupole coupling constant (QCC) NQR chemical shift (δ), chemical shift anisotropy (CSA), asymmetry parameter (η), NMR and hyperfine coupling constant (A), EPR was performed and the electronic effects (polarisation and delocalisation) were revealed and compared. Biological activity of thiazides has been found to depend on many factors, but mainly on the physico-chemical properties whose assessment was possible on the basis of electron density determination in the molecules performed by experimental and theoretical methods.

Sb NQR Study of Ferromagnetic Instability in Alkaline-Earth-Filled Skutterudites SrFe4Sb12 and BaFe4Sb12

Abstract: We report a 121,123 Sb nuclear quadrupole resonance (NQR) study of SrFe 4 Sb 12 and BaFe 4 Sb 12 . The absence of hyperfine splitting or marked broadening in NQR spectra even at the lowest temperature (1.5 K) suggests the absence of uniform ferromagnetic ordering in both compounds. The nuclear spin-lattice relaxation rate divided by temperature, 1/ T 1 T , does not follow the Korringa law, but shows a broad maximum at around 60 K. At temperatures higher than 80 K, 1/ T 1 T can be decomposed into two terms, (1/ T 1 T ) 0 =const. and T -dependent (1/ T 1 T ) spin . The component (1/ T 1 T ) spin is proportional to χ spin , which suggests that the present system is close to ferromagnetic instability, whereas below 60 K, (1/ T 1 T ) spin decreases to zero, being unexpected in typical nearly or weakly ferromagnetism.

101Ru NQR and hidden order in URu2Si2

Abstract: The still unclarified hidden order phase below T 0 =17.5 K in the heavy-electron system URu 2 Si 2 has been studied by 101 Ru NQR on a single crystal under H ext =0 and ambient P . Considering an i...

Sb-NQR probe for multipole degree of freedom in the first Pr-based heavy-fermion superconductor PrOs$_{4}$Sb$_{12}$

Abstract: We report $^{121,123}$Sb nuclear quadrupole resonance (NQR) measurements in the filled-skutterudite superconductor PrOs$_4$Sb$_{12}$ in the temperature range of 0.05-30 K. The electric field gradients (EFG), $V_{zz}$ and $V_{xx}-V_{yy}$, at the Sb site exhibit unusual temperature dependence below 30 K. To explain these features, we discuss the coupling between the Sb nuclear quadrupole moment and Pr $4f^2$-derived multipole moments. The observed $T$ dependence of EFG is well explained by the CEF quasi-quartet consisted of $\Gamma_1$ singlet and $\Gamma_4^{(2)}$ triplet states in the cubic point group $T_h$. These results, in turn, are indicative of the importance of the coupling between the $^{121,123}$Sb quadrupole moments and the hexadecapole moment caused by the quasi-quartet.

Molecular dynamics studies of vitreous boron oxide

Abstract: 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 B 2 O 3 ( v -B 2 O 3 ) is built up predominantly by planar B 3 O 6 rings. Most Molecular Dynamics (MD) studies can be better understood by a continuous random network of BO 3 . In this work the structure of v -B 2 O 3 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 (B 3 O 6 versus BO 3 ). 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%.

Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs4Sb12: Sb-NQR Study

Abstract: We have carried out nuclear quadrupole resonance (NQR) measurements in the filled skutterudite compounds Pr(Os 1- x Ru x ) 4 Sb 12 ( x =0.1, 0.2), in order to gain insights into the symmetry of the superconducting gap function. Upon replacing Os with Ru, the spin–lattice relaxation rate 1/ T 1 becomes proportional to temperature ( T ) at low T far below T c , and the magnitude of (1/ T 1 T ) low- T increases with increasing Ru content. These results indicate that a finite density of states is induced at the Fermi level by the impurity, and thus suggest that there exist nodes in the gap function of PrOs 4 Sb 12 .

Use of two or more sensors in a nuclear quadrupole resonance detection system to improve signal-to-noise ratio

Abstract: The use of two or more sensors tuned to the same nuclear quadrupole resonance frequency and detecting the nuclear quadrupole resonance signal results in improved signal-to-noise ratio and therefore improved nuclear quadrupole resonance detection system performance.

Ab initio calculations of vibronic activity in phosphorescence microwave double resonance spectra of p-dichlorobenzene

Abstract: The phosphorescence spectrum of p-dichlorobenzene has been calculated using multiconfiguration self-consistent-field wave functions and the quadratic response technique. Attention has been paid to the intensity distribution of the singlet–triplet (3B1 u →1A g ) transition through a number of vibronic subbands. The second order spin–orbit coupling (SOC) contribution to the spin splitting of the 3B1 u (3ππ*) state is found to be almost negligible, and the calculations therefore provide a good estimate for the zero-field splitting (ZFS) parameters based only on the electron spin–spin coupling expectation values. Nuclear quadrupole resonance constants for the different Cl isotopes are also calculated to accomplish the ZFS assignment. The electric dipole activity of the spin sublevels in the triplet–singlet transitions to the ground-state vibrational levels is estimated by calculations of derivatives using distorted geometries which are shifted from the equilibrium position along different vibrational modes. A vibrational analysis of the phosphorescence spectrum, based on the SOC-induced mixing of the singlet and triplet states calculated along different vibrational modes, provides reasonable agreement with experimental data.