Showing papers on "Nuclear quadrupole resonance published in 1990"
TL;DR: In this paper, the spin-lattice relaxation time of three nuclear species in the superconducting composition range of YBa(2)Cu(3)O(6+x) (0.4 + 1.0) was analyzed in terms of mean-field models incorporating short-range antiferromagnetic order.
Abstract: Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) results for copper-63, oxygen-17, and yttrium-89 nuclei in the superconducting composition range of YBa(2)Cu(3)O(6+x) (0.4
76 citations
TL;DR: In this article, the authors analyzed NQR/NMR in high T c oxides and showed quantitatively that 17 (1/T 1 ), 89 (1 /T 1 ) and the approximate T -linear behavior of 63 ( 1 / T 1 ) at higher temperatures can be associated with the same d-spin fluctuations around q ∼ 0.
Abstract: Nuclear relaxation experiments of 63 Cu, 17 O and 89 Y NQR/NMR in high T c oxides have been analyzed within the frame of a phenomenological model proposed by Mila and Rice, supposing that only one spin freedom exists. It was shown quantitatively that 17 (1/ T 1 ), 89 (1/ T 1 ) and the approximate T -linear behavior of 63 (1/ T 1 ) at higher temperatures can be associated with the same d-spin fluctuations around q ∼0. The anisotropy data of 63 (1/ T 1 ) were also explained consistently, from which the values of hyperfine coupling constants were determined. The contribution of antiferromagnetic d-spin fluctuations to 63 (1/ T 1 ) was extracted from raw data without any adjustable parameters . The saturated value of it above ∼150 K is by an order of magnitude lower than that estimated in a localized moment scheme. A possible interplay between magnetism and superconductivity is also discussed.
71 citations
TL;DR: In this paper, the deuterium localization in a triangle-shaped potential well in the plane perpendicular to the N-D bond direction has been investigated in terms of a localization of the NQR spin-lattice relaxation rate.
Abstract: The $^{35}\mathrm{Cl}$ nuclear quadrupole resonance (NQR) and the quadrupole perturbed $^{2}\mathrm{D}$ NMR have been investigated in (${\mathrm{ND}}_{4}$)${\mathrm{TeCl}}_{6}$ in the temperature range 4.2\char21{}85 K. The $^{2}\mathrm{D}$ spin-lattice relaxation rate shows a classical maximum at about 80 K and a broad peak at about 25 K, which is attributed to the influence of a phase transition at the same temperature. An extra contribution to the chlorine NQR spin-lattice relaxation rate is observed near the cubic-to-trigonal transition at 85 K. The disappearance of the NQR signal before the second transition at about 42 K is accompanied by a divergence of the spin-spin relaxation rate. The results are discussed in terms of a localization of the deuterium in a triangle-shaped potential well in the plane perpendicular to the N-D bond direction.
45 citations
TL;DR: In this article, the site symmetry and site multiplicity of the guest molecule in clathrates were determined by NQR spectroscopy and by x-ray crystallography.
Abstract: The {sup 35}Cl nuclear quadrupole resonance (NQR) spectra of CCl{sub 4} in more than 20 clathrates have been measured in the range 4-200 K. The crystal structures of CCl{sub 4}/Dianin's compound (1), CCl{sub 4}/Fe(AcAc){sub 3} (3), CCl{sub 4}/Ni(SCN){sub 2}(3-MePy){sub 4} (4), and CCl{sub 4}/Ni(exan){sub 2}(4,4{prime}-dm-2,2{prime}-bpy) (19) clathrates are also reported. Site symmetry and site multiplicity of the guest molecule in clathrates were determined by NQR spectroscopy and by x-ray crystallography. The degree of host-guest interaction was estimated from the NQR frequency shifts. The libration frequencies of the guest molecules in trigonal cavities were determined from NQR frequencies by Bayer-Kushida theory analysis.
45 citations
TL;DR: In this article, a dc superconducting quantum interference device (SQUID) based magnetic resonance spectrometer was proposed for measurements in the frequency range of 100 kHz to several megahertz.
Abstract: We describe a dc superconducting quantum interference device (SQUID) based magnetic resonance spectrometer particularly suited to measurements in the frequency range of 100 kHz to several megahertz. Results are presented for nuclear quadrupole resonance (NQR) of boron‐11 in boron nitride at 4.2 K, yielding ωQ =1467±2 kHz. We also present a direct measurement of the methyl group tunneling frequency, ωt =210±10 kHz, of propionic acid in low field, at 4.2 K.
40 citations
TL;DR: The 35 Cl nuclear quadrupole resonance spectrum of a single crystal of sodium chlorate rotating about two axes reflects a non-Abelian gauge potential, an example of Wilczek and Zee's generalization of Berry's phase to the adiabatic transport of degenerate states.
Abstract: The 35 Cl nuclear quadrupole resonance spectrum of a single crystal of sodium chlorate rotating about two axes reflects a non-Abelian gauge potential. This gauge potential is an example of Wilczek and Zee's generalization of Berry's phase to the adiabatic transport of degenerate states
38 citations
TL;DR: In this article, a consistent explanation of the electric field gradients at Cu and O nuclei in YBa 2 Cu 3 O 7 is obtained provided that on-site 3 d and 2 p holes give the dominant contributions.
Abstract: A consistent explanation of the electric field gradients at Cu and O nuclei in YBa 2 Cu 3 O 7 is obtained provided that on-site 3 d and 2 p holes give the dominant contributions. The number of holes per Cu(2) site in the planer d x 2 - y 2 - p σ antibonding orbital is estimated to be nearly one (that is, the orbital is nearly half-filled), more than half of which are attributed to the oxygen 2 p holes. For oxygen sites, it is necessary to consider both the p σ and p π holes, while more than 80% of 2 p holes reside on the p σ orbitals in all oxygen sites.
37 citations
TL;DR: In this paper, an anomalous decrease in the NQR frequency and relaxation rate in the vicinity of the antiferromagnetic ordering temperature (TN) was observed in the case of CuO.
Abstract: Cu‐nuclear quadrupole resonance (NQR) frequency and relaxation rates measurements in CuO, in the vicinity of the antiferromagnetic ordering temperature TN, are presented. As T→T+N divergent behaviors of the relaxation rates T−11,2 and an anomalous decrease in the NQR frequency are observed. These effects are discussed in light of the temperature dependence expected for conventional one‐dimensional Heisenberg paramagnet and some anomalies are interpreted as possible results of valence fluctuations in the CuO bond character.
35 citations
TL;DR: In this paper, the transition of valence de premier ordre is studied in a spin-reseau and determination of the temperature de transition is determined in partir des analyses de la frequence de resonance and du temps de relaxation spin-resume.
Abstract: Etude de la transition de valence de premier ordre. Determination de la temperature de transition a partir des analyses de la frequence de resonance et du temps de relaxation spin-reseau
35 citations
TL;DR: In this article, two new two-dimensional nuclear quadrupole resonance experiments are discussed, both based on the principle of nutation spectroscopy, which can be used to determine the asymmetry parameter, and thus the full quadrupolar tensor, of spin-3/2 nuclei at zero applied magnetic field.
Abstract: Abstract We discuss two new two-dimensional nuclear quadrupole resonance experiments, both based on the principle of nutation spectroscopy, which can be used to determine the asymmetry parameter, and thus the full quadrupolar tensor, of spin-3/2 nuclei at zero applied magnetic field. The first experiment is a simple nutation pulse sequence in which the first time period (t1) is the duration of the radiofrequency exciting pulse; and the second (t2) is the normal free-precession of a quadrupolar nucleus at zero-field. After double Fourier-transformation, the result is a 2 D spectrum in which the first frequency dimension is the nutation spectrum for the quadrupolar nucleus at zero-field. For polycrystalline samples this sequence generates powder lineshapes; the position of the singularities, in these lineshapes can be used to determine the asymmetry parameters η in a very straightforward manner, η has previously only been obtainable using Zeeman perturbed NQR methods. The second sequence is the same nutation experiment with a spin-echo pulse added. The virtue of this refocussing pulse is that it allows acquisition of nutation spectra from samples with arbitrary inhomogeneous linewidth; thus, asymmetry parameters can be determined even where the quadrupolar resonance is wider than the bandwidth of the spectrometer. Experimental examples of 35Cl, 81Br and 63Cu nutation and nutation-echo spectra are presented.
34 citations
TL;DR: In this article, the first NQR imaging experiment on quadrupolar nuclei in a powdered solid was reported, and the results showed that the experiment was shown to be successful.
TL;DR: In this article, a continuous wave nuclear quadrupole resonance spectrometer with a high sensitivity even at low frequencies has been built for detecting boron NQR in a glass.
TL;DR: In this article, it was shown that strongly hydrogen bonded complexes reveal, in a critical donor-acceptor range, a number of anomalies such as very low values of the IR frequencies of the protonic bands, stepwise increase of the polarity expressed by the dipole moment (solution) or nuclear quadrupole resonance frequency (solid), maximum value of proton magnetic resonance.
TL;DR: In this paper, the authors measured the Cu nuclear quadrupole resonance (NQR) spectrum at 100 K in YBa 2 Cu 4 O 8± y doped with 10% Ca (T c = 91 K ).
Abstract: For the understanding of the T c enhancement in Ca doped YBa 2 Cu 4 O 8± y it is crucial to know which crystallographic site the Ca +2 ion is occupying. We investigated this problem by measuring the Cu nuclear quadrupole resonance (NQR) spectrum at 100 K in YBa 2 Cu 4 O 8± y doped with 10% Ca ( T c = 91 K ). The NQR lines of the plane and chain Cu sites appear at the same frequencies v q as in the pure compound, however, both lines are broadend by static defects. Within the linewidths no temperature dependence of v q was observed and no indication for magnetic ordering at the Cu sites was found. At 20 600 Mhz, near to the Cu(1) line, a resonance line has been detected which is absent in the pure YBa 2− x Ca x Cu 4 O 8± y spectrum. Based on NQR arguments we assign this new line to Cu(1) nuclei whose electric field gradients are disturbed by Ca +2 ions occupying Ba +2 sites. We concluded that a major fraction of Ca ions occupy Ba sites, therefore the increase of T c by Ca doping cannot be explained by an increase of the hole concentration.
TL;DR: A high-order adiabatic-approximation method to study the time evolution of degenerate quantum-mechanical systems with slowly changing Hamiltonians is proposed and nonadiabatic corrections for problems in the second-order approximation are given.
Abstract: A high-order adiabatic-approximation method is proposed to study the time evolution of degenerate quantum-mechanical systems with slowly changing Hamiltonians. We not only discuss the quantum adiabatic theorem, induced gauge structure, and non-Abelian Berry's phase factors in the first-order approximation, but we also give nonadiabatic corrections for problems in the second-order approximation. With the nuclear quadrupole resonance as an explicit example, we analyze the above-mentioned questions in detail and point out the observable effects of non-Abelian Berry's phase factors for nonadiabatic transitions between two instantaneous states in an improvement of Tycko's experiment.
TL;DR: In this paper, pure nuclear quadrupole resonance (NQR) studies of 10B and 11B in borate glasses have been accomplished, yielding values of the quadrupolar parameters (the coupling constant Qcc and the asymmetry parameter ν) that are an order of magnitude more accurate than those obtained from analysis of quadrupolae effects in nuclear magnetic resonance spectra.
Abstract: Pure nuclear quadrupole resonance (NQR) studies of 10B and 11B in borate glasses have been accomplished. The data yield values of the quadrupolar parameters (the coupling constant Qcc and the asymmetry parameter ν) that are an order of magnitude more accurate than those obtained from analysis of quadrupolar effects in nuclear magnetic resonance (NMR) spectra. The linewidth of the 11B spectrum (at 1.35 MHz) for crystalline B2O3 is 9.6 ± 0.1 kHz, and the value for vitreous B2 is only 22.3 ± 0.1 kHz. Two 11B responses separated by about 50 kHz are found for vitreous B2O3. They arise from borons in boroxol rings (∼ 85%) and chains of BO3 triangles (∼ 15%). The data are obtained at 77 K with an extremely sensitive regenerative oscillator of the Robinson type.
TL;DR: In the superconducting La2CuO4+δ obtained by annealing in high pressure mixture gas of oxygen and argon, nuclear quadrupole resonance (NQR) signals of 63Cu and 65Cu have been observed around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signal around 70-100 MHz as discussed by the authors.
TL;DR: In this paper, the authors investigated the phase transitions in tris (methylammonium) nonabromodiantimonate (III), (CH3NH3)3 Sb2Br9, and its partially deuterated analog, (CH 3ND3) 3 Sb 2Br9 by measuring the temperature dependences of static and rotating frame proton spin-lattice relaxation times (T1 and T1Q), the deuteron lineshapes, 81Br NQR frequencies, and nuclear quadrupole spin−latt
Abstract: Molecular motions and phase transitions in tris (methylammonium) nonabromodiantimonate(III), (CH3NH3)3 Sb2Br9, and its partially deuterated analog, (CH3ND3)3 Sb2Br9, are investigated by measuring the temperature dependences of static and rotating frame proton spin–lattice relaxation times (T1 and T1Q), the deuteron lineshapes, 81Br NQR frequencies, and nuclear quadrupole spin–lattice relaxation times (T1Br). Discontinuities in the spin–lattice relaxation plots confirm the existence of three different phase modifications related to a freezing of reorientation of methylammonium cations. Molecular motions occurring in the respective phases are identified and their activation energies are determined. 2D NMR spectra show that the methylammonium cations are in phase I isotropically disordered possessing dynamically almost spherical symmetry, whereas at low temperature phase III the cations reorient only along the C3-axis. The role of N–H … Br hydrogen bonds and the effect of 1H 2D isotope substitution on the phase transition temperatures, activation energies of methylammonium groups, and 81Br NQR frequency isotope shifts are discussed. The NQR and NMR results pertaining to the three phases are discussed and related to other studies.
Molekulbewegungen und Phasenubergange in tris-(Metylammonium) nonabromodiantimonat(III) (CH3NH3)3 Sb2Br9 und sein teilweise deuteriertes Analogon, (CH3ND3)3 Sb2Br9 werden durch Messung der Temperaturabhangigkeiten der statischen Relaxationszeit und der Relaxationszeit im rotierenden Koordinatensystem (T1 und T1Q), der Deuteronenlinienformen, 81Br-Kernresonanzfrequenzen und der Kernquadrupol-Spin–Gitter-Relaxationszeiten (T1Br) untersucht. Die Kontinuitaten in den Darstellungen der Spin–Gitterrelaxation bestatigen die Existenz von drei unterschiedlichen Phasenmodifikationen, die mit einem Ausfrieren der Umordnung von Methylammoniumkationen verbunden sind. Molekulbewegungen, die in den entsprechenden Phasen auftreten, werden identifiziert und ihre Aktivierungsenergien bestimmt. 2D-Kernresonanzspektren zeigen, das die Methylammoniumkationen in Phase I isotrop fehlgeordnet sind und dynamisch fast spharische Symmetrie besitzen, wahrend in der Niedertemperaturphase III die Kationen sich nur in Richtung der C3-Achse umorientieren. Die Rolle der NH … Br Wasserstoffbanden und der Einflus der 1H 2D-Isotopensubstitution auf die Phasenubergangstemperaturen, Aktivierungsenergien der Methylammoniumgruppen und 81Br-Kernresonanz-Isotopenverschiebungen werden diskutiert. Die Kernquadrupol- und Kernresonanzergebnisse, die zu den drei Phasen gehoren, werden diskutiert und mit anderen Untersuchungen verknupft.
TL;DR: In this article, the nuclear quadrupole resonance frequency temperature dependence for a variety of chemical systems is observed to behave linearly in T 2 over a wide range of temperatures, which leads to the formulation of an empirical master equation.
TL;DR: In this paper, the authors observed the temperature and the x -dependence of the 139 La-NQR spectra in magnetically ordered La 2- x Ba x CuO 4, showing that the internal field at La nuclei increases discontinuously at T c *, where the nuclear relaxation rate is enhanced and shows its peak.
Abstract: We observed the temperature and the x -dependence of the 139 La-NQR spectra in magnetically ordered La 2- x Ba x CuO 4 . The internal field at La nuclei increases discontinuously at T c * , where the nuclear relaxation rate is enhanced and shows its peak. This indicates that a successive magnetic transition occurs at T c * for x <0.02. An asymmetry parameter of the electric quadrupole interaction changes anomalously at the magnetic transition. The magnetic phase diagram of the La-system is discussed.
TL;DR: In this paper, the transverse relaxation of the planar Cu(2) nuclear spins in an oriented powder sample of YBa 2 Cu 3 O 6.98 (T c =92 K) was measured using the nuclear quadrupole resonance (NQR) technique.
Abstract: We have measured the transverse relaxation of the planar Cu(2) nuclear spins in an oriented powder sample of YBa 2 Cu 3 O 6.98 ( T c =92 K) by using the nuclear quadrupole resonance (NQR) technique. Above T c , after subtraction of the T 1 process, the spin echo envelope decay follows a Gaussian form, and its time constant is almost independent of temperature. In the vicinity of T c , however, the Gaussian line shape is gradually narrowed. The calculated value ( T G =149 µsec) for the Gaussian time constant based on the direct nuclear dipole-dipole interaction is comparable to the experimental one ( T G =131±2 µsec) at 297 K. Hence, the nuclear indirect coupling proposed previously may not be needed. Below T c , the Gaussian line shape was found to be narrowed depending on H 1 , and especially, it is sharply narrowed at 35 K and 87 K.
TL;DR: In this article, the temperature dependence of the 14 N and 17 O NQR frequencies has been measured in N-5-chlorosalicylideneaniline with the help of nuclear quadrupole double resonance.
TL;DR: In this paper, the IR and 35 Cl NQR spectra of several solid hydrogen-bonded adducts of o-chlorobenzoic acids and amines were studied over the broad ΔPk a range.
Abstract: The IR and 35 Cl NQR spectra of several solid hydrogen bonded adducts of o-chlorobenzoic acids and amines were studied over the broad ΔPk a range. Both IR and NQR spectra yield the indication of the existence of an inversion (critical) ΔpK a range where the proton transfer takes place. The critical point is distinguished by a deep minimum of the position of the gravity centre of the broad protonic band
TL;DR: Connor et al. as discussed by the authors reported the application of dc SQUID (superconducting quantum interference device) spectrometer to nuclear quadrupole resonance (NQR) studies of aluminum•27 and boron•11 in crystalline and glassy solids.
Abstract: We report the application of our dc SQUID (superconducting quantum interference device) spectrometer [C. Connor, J. Chang, and A. Pines, Rev. Sci. Instrum. 61, 1059(1990)] to nuclear quadrupole resonance (NQR) studies of aluminum‐27, and boron‐11 in crystalline and glassy solids. Our results give e2qQ/h=2.38 MHz and η=0.0 for α–Al2O3 at 4.2 K. For the natural mineral petalite (LiAlSi4O10), we obtain e2qQ/h=4.56 MHz and η=0.47. The quadrupole resonance frequency is 1467 kHz in boron nitride, and in the vicinity of 1300 kHz for various borates in the B2O3⋅xH2O system. The distribution of boron environments in a B2O3 glass gives rise to a linewidth of about 80 kHz in the SQUID detected resonance.
TL;DR: The temperature dependence of the nuclear transverse relaxation rate, 1/T 2, of Cu-NQR in YBa 2 Cu 3 O 7- y and La 2- x Sr x CuO 4 is measured in the superconducting and the normal states as mentioned in this paper.
Abstract: The temperature dependence of the nuclear transverse relaxation rate, 1/ T 2 , of Cu-NQR in YBa 2 Cu 3 O 7- y and La 2- x Sr x CuO 4 is measured in the superconducting and the normal states The anomalous enhancement of 1/ T 2 at the Cu(1) and Cu(2) sites is observed at 35 K in YBa 2 Cu 3 O 7- y but is not observed in the superconducting La 2- x Sr x CuO 4
TL;DR: In this article, the authors show that the magnetic Cu moments exist only at the Cu-O pyramidal site with the 3 d 9 state and that the Cu ion at the oxygen-free plane site is nonmagnetic ( d 10 ) in the insulating Pb 2 Sr 2 RECu 3 O 8+δ.
Abstract: Nuclear magnetic resonance of 63/65 Cu in the antiferromagnetic Pb 2 Sr 2 RECu 3 O 8+δ (RE=Y, Eu and Gd) was observed in zero external field. In the insulating state with antiferromagnetically ordered Cu moments, the other set of NQR signals was observed around 30 MHz, indicating that the transferred hyperfine field from Cu moments in the Cu-O pyramids is canceled out at the Cu nuclei in the oxygen-free Cu plane site. The results show that the magnetic Cu moments exist only at the Cu-O pyramidal site with the 3 d 9 state and that the Cu ion at the oxygen-free plane site is nonmagnetic ( d 10 ) in the insulating Pb 2 Sr 2 RECu 3 O 8+δ .
TL;DR: In this paper, the Fourier transform of the amplitude of the free induction decay of the central transition after the second of two sufficiently short (nonselective) RF pulses as a function of their time distance was shown to yield simplified first-order quadropolar solid-state nuclear magnetic resonance spectra from which the quadropole frequency and asymmetry parameter can be easily determined.
TL;DR: In this paper, the antiferromagnetic order at the Cu(2) sites appears either at low oxygen concentration or for RE = Pr. In both cases no ordered magnetic moments exist at the CU(1) sites.
TL;DR: In this article, the spin alignment of Cu moments in the CuO 2 plane changes at a critical concentration of the substitution of Cu by T. The spin structure of the low-temperature magnetic phase is discussed.
Abstract: Split spectra of Cu nuclear quadrupole resonance (NQR) in the chain (Cu(1)) site of the antiferromagnetic YBa 2 (Cu 1- x T x ) 3 O 6 (T=Fe, Co, and Ni) show that the spin alignment of Cu moments in the CuO 2 plane changes at a critical concentration of the substitution of Cu by T. The spin structure of the low-temperature magnetic phase is discussed.
01 Feb 1990
TL;DR: In this paper, a correlation between the 35Cl NQR frequencies and Sn-Cl bond lengths was found for 42 tin compounds, where nQR and crystal structure data were known.
Abstract: The 35Cl NQR spectra of two complexes of dichlorodimethylstannane, Me2SnCl2 · 2L (L = N,N-dimethylformamide(I) and dimethyl sulfoxide(II), respectively), have been recorded as a function of temperature between 225 K and 350 K for (I) and between 216 K and 377 K for (II). A correlation between the 35Cl NQR frequencies and Sn — Cl bond lengths was found for 42 tin compounds, where NQR and crystal structure data are known. The correlation can either be described by the linear relation v(35Cl) = −0.42(6) MHz/pm · d(Sn — Cl) + 118(15) MHz (correlation coefficient r = -0.937) or by the relation v(35Cl) = 5.3(8) · 108 MHz · pm3 · d−3(Sn — Cl) — 22(5) MHz (r = 0.938). The reliability of the correlation v(35Cl) = f(d(Sn — Cl)) is discussed.