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Showing papers on "Nuclear quadrupole resonance published in 2000"


BookDOI
01 Jan 2000
TL;DR: The literature published up to late 1984 includes nuclear magnetic resonance, nuclear quadrupole resonance spectroscopy, rotational spectroscopic properties of compounds of main-group elements, vibrational spectra of transition-element compounds and some co-ordinated ligands, and gas-phase molecular structures determined by electron diffraction as mentioned in this paper.
Abstract: This book covers literature published up to late 1984. Includes nuclear magnetic resonance; nuclear quadrupole resonance spectroscopy; rotational spectroscopy; characteristic vibrations of compounds of main-group elements; vibrational spectra of transition-element compounds and some co-ordinated ligands; Mossbauer spectroscopy; and gas-phase molecular structures determined by electron diffraction.

120 citations


Journal ArticleDOI
TL;DR: In this article, a pulsed spectrometer for detection of nuclear quadrupole resonance on the nuclei of nitrogen N-14 with fast Fourier transform was described, and the time of detection was 81 s.
Abstract: We describe a pulsed spectrometer for detection of nuclear quadrupole resonance on the nuclei of nitrogen N-14 with fast Fourier transform. The use of a multipulse sequence, four channel system for data registration and processing permits detection of the nuclear quadrupole resonance (NQR) signal in the presence of strong interference and the piezo effect. Using this spectrometer we registered the NQR signal from an explosive sample of 150 g (92% RDX) at a distance of 22 cm, and the time of detection was 81 s.

75 citations


Journal ArticleDOI
TL;DR: In this article, the authors carried out 115In nuclear quadrupole resonance (NQR) measurements in CeRhIn5 and found that the nuclear spin lattice relaxation rate 1/T1 has no Hebel-Slichter coherence peak just below 2 K and has a power law T-dependence down to 300 mK.
Abstract: We have carried out 115In nuclear quadrupole resonance (NQR) measurements in CeRhIn5. At ambient pressure, CeRhIn5 undergoes an antiferromagnetic AF phase transition at \(\) K. The 115In NQR spectrum has shown the appearance of a small internal field in the direction perpendicular to the tetragonal c-axis. With application of a hydrostatic pressure, the AF state is suppressed and the superconductivity appears just above the critical pressure (P = 17 kbar). The nuclear spin lattice relaxation rate 1/T1 of 115In measured at P = 27 kbar indicates the occurrence of the superconductivity in the nearly AF region. In the superconducting state, 1/T1 has no Hebel-Slichter coherence peak just below \(\) of 2 K and has a power law T-dependence (T3) down to 300 mK. This is consistent with anisotropic superconductivity, with line nodes in the superconducting energy gap: non-s-wave superconductivity occurs in CeRhIn5.

57 citations


Patent
14 Jan 2000
TL;DR: A Q-damping subsystem for either an NQR or NMR detection receiver for effectively reducing the dead time and increasing sensitivity of the contraband detection system was proposed in this paper.
Abstract: A Q-damping subsystem for either an NQR or NMR contraband detection receiver for effectively reducing the dead time and increasing sensitivity of the contraband detection system. The invention acts as an addition to the standard transmit circuits of NQR and NMR based scanners and spectrometers. The active Q-damping devices require additional circuitry for an NQR/NMR detection receiver and a programming for the control thereof. Typically, the detection receiver generates a high-voltage RF pulse on the order of 200-1000 V with normal operation of 100-300 microseconds in length to provide sufficient magnetic field characteristics to perturb the precessing nuclei. The NQR or NMR detection receiver electronics are very sensitive and have to detect a very weak nuclear induction pulse signal that is in the nano/micro-volt range. The invention encompasses several embodiments of the detection receiver with the Q-damping subsystem which include: a transformer coupled resistive damping circuit; an inductively coupled resistive damping circuit; a shunt capacitor/resistor damping circuit; a grounded shunt capacitor/resistor damping circuit; a common mode choke transient suppression damping circuit; a multi-stage Q-damping circuit; and a full-wave Q-damping circuit.

53 citations


Journal ArticleDOI
TL;DR: Using Cu nuclear quadrupole resonance (NQR) in Eu-doped La2-xSrxCuO4 the authors find the evidence of the pinned stripe phase at 1.3 K for 0.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase.
Abstract: Using Cu nuclear quadrupole resonance (NQR) in Eu-doped La2-xSrxCuO4 we find the evidence of the pinned stripe phase at 1.3 K for 0. 08 0.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase.

38 citations


Journal ArticleDOI
TL;DR: Nuclear quadrupole resonance measurements have been performed on Cu(2) plane sites and Cu(1) chain sites in fully doped YBa2Cu3O7 and confirm the existence of a charge-density-wave state (CDW) in the chains.
Abstract: Nuclear quadrupole resonance (NQR) measurements have been performed on Cu(2) plane sites and Cu(1) chain sites in fully doped YBa2Cu3O7 between 300 and 4.2 K. The sharp increase of the Cu(1) NQR linewidth across the superconducting transition and the T dependence of the Cu(1) spin lattice relaxation rate confirm the existence of a charge-density-wave state (CDW) in the chains. The simultaneous broadening of the Cu(2) linewidth below T(c) and the anomalous T dependence of Cu(1) and Cu(2) NQR parameters indicate that these in-chain CDW correlations are strongly involved in the appearance of an in-plane charge modulated structure below T(c).

35 citations


Journal ArticleDOI
Y. Kohori, T Kohara, Y. Yamato, G.J. Tomka1, P.C. Riedi1 
TL;DR: In this article, the antiferromagnetic (AF) dense-Kondo compound CeIn 3 (T N = 10 K ) under pressure was measured and the nuclear spin-lattice relaxation rate T 1 −1 was nearly temperature independent in the paramagnetic state and was strongly suppressed with increasing pressure.
Abstract: We have carried out 115 In nuclear quadrupole resonance (NQR) measurements of the antiferromagnetic (AF) dense-Kondo compound CeIn 3 (T N =10 K ) under pressure. In the AF ordered state, a small internal field of about 6 kOe (1.6 K) appears in the direction parallel to the respective Ce–In planes. The non-vanishing 115 In internal field means that the Ce magnetic moments orient perpendicular to the (1 1 1) plane. With applied pressure, the internal field decreases gradually and disappears above 24.4 kbar. The nuclear spin–lattice relaxation rate T 1 −1 is nearly temperature independent in the paramagnetic state and is strongly suppressed with increasing pressure. Fermi liquid behavior was observed below 10 K at 27.4 kbar.

31 citations


Journal ArticleDOI
TL;DR: In this paper, the 14 N NQR spectrum of one gram of military grade trinitrotoluene (TNT) obtained from an abandoned land mine has been determined by 1 H- 14 N nuclear quadrupole double resonance at room temperature.
Abstract: The 14 N NQR spectrum of one gram of military grade trinitrotoluene (TNT) obtained from an abandoned land mine has been determined by 1 H- 14 N nuclear quadrupole double resonance at room temperature. The magnetic field dependence of the proton spin-lattice relaxation time T 1 as well as the 14 N T 1 of TNT were determined as well. The use of a double frequency irradiation technique allowed for a unique assignment of the twelve observed lines to the v + and v- 14 N transitions of the six chemically non-equivalent crystallographic nitrogen sites in the unit cell. Nuclear quadrupole double resonance results in an increase in the 14 N signal to noise ratio by a factor of 30 as compared to conventional NQR and a significant reduction of the measuring time which is important in the detection of explosives.

24 citations


Journal ArticleDOI
TL;DR: The two-frequency nuclear quadrupole resonance (NQR) of 14N nuclei is described for purposes of explosives detection in this article, where two applications are known: one for increasing the signal intensity and the other for improving the reliability of detection.
Abstract: The two-frequency nuclear quadrupole resonance (NQR) of14N nuclei is described for purposes of explosives detection. Two applications are known: two-frequency NQR for increasing the signal intensity, two-frequency NQR for improved reliability of explosives detection. The two-frequency experiments were carried out in hexahydro-1,3,5-trinitro-s-triazine C3H6N6O6 and sodium nitrite NaNO2 as a substitute for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocycine C4H8N8O8. The two-frequency sequences for NQR are proposed for increasing the amplitude of NQR signal and improvement of detection condition.

21 citations


Journal ArticleDOI
TL;DR: In this article, the self-diffusion coefficient of a proton is estimated to be several orders of magnitude larger than that of oxygen ions, the latter coefficient being equal to 10−13 cm2 s−1 at 490 K. The behavior of yttrium barium hydrocuprate and its oxidized form (H2YBa2Cu3O7.8) is governed by poorly studied behavior of hydrogen atoms in the lattice.
Abstract: The electric, magnetic, and physicochemical properties of yttrium barium hydrocuprate (H2YBa2Cu3O7) and its oxidized form (H2YBa2Cu3O7.8) are governed, to a large measure, by poorly studied behavior of hydrogen atoms in the lattice. The crystal chemical state and the mobility of a proton intercalated into yttrium barium cuprate have been investigated by the isotope exchange and inelastic neutron scattering techniques. By their behavior in the process of inelastic neutron scattering, a substantial fraction of protons can be considered mechanically free particles without chemical bonding with oxygen ions. The self-diffusion coefficient of a proton is estimated to be several orders of magnitude larger than that of oxygen ions, the latter coefficient being equal to 10−13 cm2 s−1 at 490 K. Considerable changes in the lattice parameters and local charge distribution in the copper-oxygen subsystem are revealed by the x-ray powder diffraction analysis and nuclear quadrupole resonance (NQR). Discrete changes in the interplanar spacings along the c axis and in the Cu NQR frequencies with a gradual variation in the degrees of hydration and oxidation indicate the formation of hydrocuprate and (or) oxyhydrocuprate in the matrix of the initial material.

19 citations


Journal ArticleDOI
TL;DR: In this paper, the results of a large number of halogen, antimony and tin containing molecules and complexes were reported, with the use of small and medium basis sets, i.e. 3-21G* and 6-31G* basis sets.
Abstract: In the present work we report the results of ab initio study, within GAUSSIAN 98, of a large number of halogen, antimony and tin containing molecules and complexes. The calculations were carried out with the use of small and medium basis sets, i.e. 3-21G* (for halogens, antimony and tin) atoms and 6-31G* basis sets (for F, Cl and Br). To demonstrate the quality of the calculations the calculated bond length and quadrupole coupling constant (QCC) were compared with the corresponding experimental values for the compounds studied. With a few exceptions, the overall agreement with experiment is most satisfactory. The calculated NQCC values were used as a test of the quality of the wave functions. The results on Mossbauer chemical shifts are also in a good agreement with the experimental data, however, these quantities were measured only for a few compounds.

Journal ArticleDOI
TL;DR: The experimental results show the presence of a fast exchange of hydrogen atoms between two nonequivalent positions within the O-H ellipsis O hydrogen bonds, ascribed to concerted jumps of two hydrogen atoms within the hydrogen bonds connecting two molecules in a dimer.

Journal ArticleDOI
TL;DR: In this paper, the oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is studied, for the first time in a comparative way, on pair samples having the same oxygen content and thermal history, but different Cu(1)Ox chain arrangements deriving from their intercalated and deintercalated nature.
Abstract: The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is studied, for the first time in a comparative way, on pair samples having the same oxygen content and thermal history, but different Cu(1)Ox chain arrangements deriving from their intercalated and deintercalated nature. Structural and electronic non-equivalence of pairs samples is detected in the critical region and found to be related, on microscopic scale, to a different average chain length, which, on being experimentally determined by nuclear quadrupole resonance (NQR), sheds new light on the concept of critical chain length for hole doping efficiency.

Journal ArticleDOI
15 Jun 2000-EPL
TL;DR: In this paper, the electric field gradient (EFG) at the central copper site of the cluster after replacing a lanthanum atom in the cluster with a strontium atom or adding an interstitial oxygen to the cluster was investigated.
Abstract: The nuclear quadrupole resonance (NQR) spectrum of strontium-doped La2CuO4 surprisingly resembles the NQR spectrum of La2CuO4 doped with excess oxygen, both spectra being dominated by a main (A) peak and one principal satellite (B) peak at similar frequencies. Using first-principles cluster calculations, this is investigated here by calculating the electric field gradient (EFG) at the central copper site of the cluster after replacing a lanthanum atom in the cluster with a strontium atom or adding an interstitial oxygen to the cluster. In each case the EFG was increased by approximately 10% leading unexpectedly to the explanation that the NQR spectra are only accidentally similar and the origins are quite different.

Journal ArticleDOI
TL;DR: In this paper, single crystal X-ray diffraction, 35Cl nuclear quadrupole resonance (NQR) and differential scanning calorimetry (DSC) measurements were taken for bis(pyrrolidinium) hexachlorometallates, (C4H8NH2)2MCl6 (M=Sn, Te and Pt).

Journal ArticleDOI
TL;DR: The phase diagram of La2-xSrxCuO4 at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02) could be more complicated than previously thought, with a transition to a quasi-long range ordered state at K, as indicated by neutron scattering data as mentioned in this paper.
Abstract: Anelastic relaxation and 139LaNQR relaxation rates in La2–xSrxCuO4 for Sr content around 2 and 3 percent are discussed in terms of spin and lattice excitations and of the related ordering processes. It is argued how the phase diagram of La2–xSrxCuO4 at the boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02) could be more complicate than previously thought, with a transition to a quasi-long range ordered state at K, as indicated by neutron scattering data. On the other hand, the 139LaNQR spectra are compatible with a transition to an AF phase around K, in agreement with the phase diagram commonly accepted in literature. In this case the peaks in NQR and anelastic relaxation rates around 150 K and 80 K respectively in La1.98Sr0.02CuO4, yield the first evidence of freezing process involving simultaneously lattice and spin excitations, possibly corresponding to motion of charged stripes.

Journal ArticleDOI
TL;DR: In this article, a wide temperature range of 300 K to 1.5 K was used to examine the possibility of the static spin-charge stripe order in La 2- x Ba x CuO 4 with x = 1/8.
Abstract: Cu-NQR spectra were measured in the wide temperature range of 300 K to 1.5 K to examine the possibility of the occurrence of the static spin-charge stripe order in La 2- x Ba x CuO 4 with x =1/8. The usual NQR spectrum is observed above T d2 , the structural transition temperature from the LTO to LTT phase. Below T d2 , the signal intensity decreases rapidly with decreasing temperature, which is accompanied with the abrupt increase of the effective spin echo decay rate, while no significant changes appear in its lineshape down to 10 K. Below 10 K, the spectrum starts to spread and exhibits unusual broadening with a tail to about 80 MHz at 1.5 K. The abnormally broad spectrum at 1.5 K, which is regarded as evidence of the static spin and/or charge order, is simulated satisfactorily in terms of the stripe order proposed for La 2- x - y Nd y Sr x CuO 4 ( x =1/8) with the assumption of the modulation amplitude for Cu moment of about 0.24 µ B .

Journal ArticleDOI
TL;DR: In this paper, a simple device intended for suppressing transient processes in the oscillatory circuit of the nuclear quadrupole resonance spectrometer operating at 0.5-10 MHz is described.
Abstract: A simple device intended for suppressing transient processes in the oscillatory circuit of the nuclear quadrupole resonance spectrometer operating at 0.5–10 MHz is described. The transient process duration is reduced by applying active damping to the circuit immediately after the excitation pulse terminates. The switching time is ≤0.1 μs. At 3.3 MHz, the transient process duration is reduced by a factor of 5.

Journal ArticleDOI
TL;DR: In this paper, a variety of two-and three-dimensional NQR experiments are reviewed, showing their application to the determination of field gradients for important sites in peptides and proteins, for assigning connected transitions of nuclei with spin ≥ 5/2, and for determining hexadecapolar coupling constants.
Abstract: A variety of two dimensional two-and three-dimensional NQR experiments are reviewed, showing their application to the determination of field gradients for important sites in peptides and proteins, for assigning connected transitions of nuclei with spin ≥ 5/2, and for determining hexadecapolar coupling constants. The quadrupole coupling tensor for 63Cu in the active site of a protein, bovine erythrocyte (Cu, Zn) superoxide dismutase, has been measured and is compared with the results of ab initio calculations.

Journal ArticleDOI
TL;DR: In this article, the effect of electron donating or repelling group substitution in the phenyl ring on the γ(35 Cl NQR of Cl(ω)) of the dichloroacetyl group was studied.
Abstract: Abstract To study the effect of electron donating or repelling group substitution in the phenyl ring on the γ(35 Cl NQR of Cl(ω)) of the dichloroacetyl group, several N-(methylsubstituted-phenyl)-2,2-dichloroacetamides have been synthesised, characterised and their 35 Cl NQR frequencies mea-sured at 77 K. All the substituted amides, except N-(2,5-dimethylphenyl)-2,2-dichloro-acetamide, show two ω-C-Cl frequencies in the range of 37.009 -38.014 MHz. N-(2,5-dimethylphenyl)-2,2-dichloroacetamide shows one u-C-C 1 NQR frequency at 37.50 MHz for the two chlorine atoms present. The two atoms may be crystallographically equivalent. The frequencies of all the methyl-substituted dichloroacetamides have been compared and correlated alongwith the corresponding chloro substituted-phenyl dichloroacetamides. The γ(35 C1 NQR) of Cl(ω) of all the N-(substituted-phenyl)-2,2-dichloroacetamides have been correlated with the NQR substituent parameters (κi), assuming additivity of the substituent effects. The frequencies are also correlated with Hammett a. The effect of ring substitution on the average 35 Cl NQR Cl(ω) frequencies of the dichloroacetyl group is not substantial, but it affects the crystal structures of the substituted compounds. Using the Ki values for various groups and ω-C-Cl NQR frequencies of N-(phenyl)-2,2-dichloroacetamide (37.195 and 37.596 MHz), 7(35 C1 NQR) of all the N-(methyl and chlorosubstitutedphenyl)-2,2-dichloroacetamides have been estimated. Similar calculations are extended to all the N-(methyl and chlorosubstitutedphenyl)-2-chloroacetamides and -2,2,2-trichloroacetamides. There is a rea-sonably good agreement between the computed and the experimental values for all the three groups of compounds. Further, γ(35 Cl NQR of Cl(ω) of all the substituted N-phenyl-chloroacetamides represented by the general formula XyC6H5- y NHCOR (where X = Cl, or CH3 , y = 1 or 2 and R = CH 2 Cl, CHCl2 or CCl3) are compared. The γ(35Cl NQR of Cl(ω)) of the substituted N-(phenyl)-2,2-dichloroacetamides lie between the frequencies of the corresponding substituted N-(phenyl)-2-chloroacetamides and substituted N-(phenyl)-2,2,2-trichloroacetamides.


Journal ArticleDOI
TL;DR: In this paper, a fully automated PC-controlled pulsed FT NQR spectrometer equipped with a large volume (70 1) radio-frequency (RF) sample coil to accommodate a typical suitcase is presented.
Abstract: Nuclear quadrupole resonance (NQR) of14N nuclei has many advantages as a method for detecting nitrogen-containing explosives, the most important are very high chemical specificity, true noninvasive operation and detection of bulk explosive in situ only (no vapor or particular capture needed). One of the most high explosives is hexogen (RDX) often used by terrorists in plasticized forms. The ring nitrogen nuclei in an RDX molecule generate three sets of NQR frequencies corresponding to three physically nonequivalent positions of the molecule in the crystal lattice. The prototype device we have constructed is intended for inspection of suitcases for the presence of plastic explosives containing RDX or octogen by14N quadrupole resonance. It is essentially a fully automated PC-controlled pulsed FT NQR spectrometer equipped with a large volume (70 1) radio-frequency (RF) sample coil to accommodate a typical suitcase. The device consists of a measure chamber with an RF coil, tuning and matching box, an RF pulse transmitter and a control PC with dedicated cards like digital receiver, frequency synthesizer, pulse programmer and probe-tuning controller. The control software finds the NQR lines and measures their frequencies. An alarm is produced if any of these frequencies matches the characteristic NQR frequency of the explosive and the signal-tonoise ratio exceeds the preset threshold. Multipulse sequences of the type SORC (strong off-resonance comb) or SLSE (spin-locked spin echo) were used in order to increase the allowed data acquisition rate. We could detect 230 g of PMW-8, a plastic explosive (containing 81% of RDX) in 10 s or 100 g in 30 s. Detection probability was not less than 90%.

Journal ArticleDOI
TL;DR: In this article, the authors report the NQR on Ba nuclei in four samples of BaBiO 3 prepared in different ways and report the spectra of 137 Ba consist of broad line centered near 18 MHz at 42 K.
Abstract: We report the NQR on Ba nuclei in four samples of BaBiO 3 prepared in different ways The spectra of 137 Ba consist of broad line centered near 18 MHz at 42 K The broadening of NQR suggests a local distortions of the crystal structure The area under the line for ceramic sample BaBiO 3 synthesized at 800°C is approximately two times larger comparing to ceramic samples and single crystal prepared at 930–1080°C The decrease of the NQR signal is attributed to the partial disordering of charge disproportionating Bi ions on the two inequivalent sites

Journal ArticleDOI
TL;DR: In this paper, the authors present results of 35Cl NQR and 1H NMR measurements of thiourea-hexachloroethane, [2.95(NH2)2CS]C2Cl6, in the temperature range from 7.5 to 90 K, which confirm the existence of such a state at least below 60 K.
Abstract: Atom-atomic potential calculation of the channel non-stoichiometric thiourea-hexachloroethane inclusion compound shows that the structure of the guest sublattice comprises two types of finite molecular chain, having different structure and separated by domain walls. In the present paper we present results of 35Cl NQR and 1H NMR measurements of thiourea-hexachloroethane, [2.95(NH2)2CS]C2Cl6, in the temperature range from 7.5 to 90 K, which confirm this model and show the existence of such a state at least below 60 K. Two resonances in the NQR spectra were assigned to the two nearly commensurate regions, while the third resonance, showing an anomalous behaviour, was attributed to the guest molecules in the domain wall. The observed structure results from the different periodicity of the guest and host substructures and shows a difference from conventional continuum models of the incommensurate state. Propagation motion of the domain wall over the channel is discussed.

Journal ArticleDOI
TL;DR: In this article, a distortion field function (DFF) was used to fit nuclear quadrupole resonance line shapes in solids, based on the existence of a DFF describing the local order properties of the condensed phase.

Journal ArticleDOI
TL;DR: In this article, a nuclear quadrupole resonance of the in-plane Cu of YBa 2 Cu 3 O y ( y = 6.61) has been carried out to investigate if the “wipeout” phenomenon, which is observed in La 2- x - y Nd y Sr x CuO 4 and La 2 - x - nd y S 4 and is considered to be related to the slowdown of the charge fluctuation and possibly to the "stripe" formation, can also be found for the system in the 60 K plateau region of the
Abstract: Nuclear quadrupole resonance of the in-plane Cu of YBa 2 Cu 3 O y ( y =6.61) has been carried out to investigate if the “wipeout” phenomenon, which is observed in La 2- x - y Nd y Sr x CuO 4 and La 2- x Sr x CuO 4 and is considered to be related to the slowdown of the charge fluctuation and possibly to the “stripe” formation, can also be found for the system in the 60 K plateau region of the oxygen number y . No evidence for such a phenomenon has been found, indicating that the origin of the plateau cannot easily be connected to the existence of the fluctuating “stripe” in the system.

Journal ArticleDOI
TL;DR: In this article, the dependence of the Maki-Thompson and of the density of states depletion contributions from superconducting fluctuations to nuclear magnetic resonance and nuclear quadrupole resonance relaxation is derived in the framework of the diagrammatic theory, applied to layered three-dimensional (3-D) high-Tc superconductors.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this paper, two kinds of partially overlapping Ni NMR spectra were observed in Ce7Ni3 containing an enriched 61Ni, which indicates that the systems are in the Fermi liquid state at ambient pressure.
Abstract: The heavy fermion compound Ce7Ni3 is an antiferromagnet with TN∼1.7 K. According to the high pressure experiment, this compound has undergone a transition to a non-Fermi liquid state at ∼0.32 GPa and has recovered a Fermi liquid state at ∼0.62 GPa again. Before the high pressure nuclear magnetic resonance (NMR) study through two transitions, we have performed NMR experiments of 61Ni, 59Co and 63Cu in order to clarify the electronic states at ambient pressure. Two kinds of partially overlapping Ni NMR spectra were observed in Ce7Ni3 containing an enriched 61Ni. This result may be ascribed to two intrinsic local fields presumably due to the lattice distortion, etc. All the relaxation rates studied here are proportional to temperature above 1.4 K in the paramagnetic state, which indicates that the systems are in the Fermi liquid state at ambient pressure. The increase of (1/T1T) with increasing Co concentration, CCo, tells us that the partial density of states on Ni-3d states at Fermi level, N(EF)Ni, increas...

Journal ArticleDOI
TL;DR: In this article, the NQR spin-lattice relaxation-time minimum, ascribed to the modulation effect of the electric field gradient (EFG) due to a motion of the ammonium ions, was observed at 7 K and 11 K in NH4ICl4 and ND4 ICl4, respectively.
Abstract: Cl NQR measurements revealed two phase transitions at 14.5 K and 70 K in NH4ICl4. By deuteration of the ammonium ions, the respective transition temperature increased to 27 K and 74 K. In the lowest-temperature phase of NH4ICl4, by the deuteration a remarkable change of the temperature dependence of the Cl NQR frequencies was observed. The NQR spin-lattice relaxation-time minimum, ascribable to the modulation effect of the electric field gradient (EFG) due to a motion of the ammonium ions, was observed at 7 K and 11 K in NH4ICl4 and ND4ICl4, respectively. The activation energy of the ammonium motion and the fluctuation fraction q0=q of the EFG were determined to be 0.32 kJ mol 1 and 1.3 10 3 for NH4ICl4, and 0.30 kJ mol 1 and 0.88 10 3 for ND4ICl4. The experimental result suggests that the inter-ionic interaction between the ammonium ion and the ICl 4 complex anion is weakened by the deuteration. However, the frequency shift observed in the lowest-temperature phase is much larger in ND4ICl4 than in NH4ICl4. This suggests that the lattice distortion in NH4ICl4 is suppressed to a great deal by the tunneling rotation of NH4 ions. The effective inter-ionic interaction responsible for the lattice distortion, the transition temperature and the enhancement of tunneling of NH4 as compared with ND4 is discussed for NH4ICl4 as well as for previously reported NH4AuCl4 and -NH4HgCl3.

Journal ArticleDOI
TL;DR: In this paper, NMR and NQR signals of two different crystallographic Mn sites, which are in nearly axial and nonaxial electric field gradients, were found below structural transitions, being consistent with the crystal structure determined from diffraction analysis and confirming the absence of magnetic ordering.
Abstract: We performed ${}^{55}\mathrm{Mn}$ NMR and nuclear quadrupole resonance (NQR) measurements of a cubic Laves-phase compound ${\mathrm{UMn}}_{2},$ which shows structural instability in the temperature range 210--240 K. NMR and NQR signals of two different crystallographic Mn sites, which are in nearly axial and nonaxial electric field gradients, were found below structural transitions, being consistent with the crystal structure determined from diffraction analysis and confirming the absence of magnetic ordering. Analysis of the Knight shift shows that the spin component of the isotropic hyperfine coupling constant does not change at the phase transitions, and the anisotropy of the Knight shift appreciably depends on temperature. The nuclear spin-lattice relaxation is not enhanced except around the structural transitions and is explained as simple conduction-electron relaxation, indicating absence of localized moments at both U and Mn sites. The relaxation behavior also suggests neither critical behavior nor strong electron correlation in the low-temperature range.