Ordering of oxygen in halogen treated 1-2-3 systems as studied by NQR

We have investigated the low-temperature behavior of Cu NQR for iodinated RBa₂Cu₃O _x (R = Y, Gd) compounds. The different influence of Gd spins on the Cu(1) and Cu(2) sites was used to separate the contributions of both sites in the spectra. The distinct NQR lines associated with the different oxygen-coordinated Cu(1) sites have been observed. The NQR spectra of the Cu(1) sites show that the iodine treatment gives rise to the modifications of the oxygen sublattice. From the analysis of the NQR spectra of the Cu(1) sites follows an increase of the average length of the Cu(1)-O chains at treatment.     

63Cu NQR in copper (II) compounds

We report observations of ⁶³Cu NQR in CuF₂, KCuF₃, and RbCuF₃ in the paramagnetic state, NQR line widths of ⁶³Cu in CuF₂ and CuBr₂ and of ⁸¹Br in CuBr₂, SnBr₂ and ZnBr₂. The NQR resonances of certain Cu (II) paramagnetic compounds are exchange-narrowed to values commensurate with linewidths of the diamagnetic infinite-lattice compounds.     

Cu chemistry of YBa2Cu3O6+x investigated by nuclear quadrupole resonance

The nuclear quadrupole resonance (NQR) technique has been utilized to characterize the local oxygen coordination of inequivalent Cu sites in YBa₂Cu₃O_6+x(0 ≤ x ≤ 0.91). Essentially, four distinct NQR lines which correspond to 2, 3,4 oxygen coordinated Cu sites in the Cu-O chains and 5 oxygen coordinated Cu sites in the Cu-O planes have been observed. The zero-field NQR frequencies of these are centered at about 30.1, 24.0, 22.0 and 31.5 MHz for ⁶³Cu, respectively. For the antiferromagnetic ordered state (x ≤ 0.3), antiferromagnetic nuclear resonance (AFNR) has been observed at 90 MHz with quadrupole splittings associated with the moment-bearing Cu sites in the Cu-O planes. The relative intensities of these resonance lines depend on the oxygen content, and this gives us a microscopic understanding of the Cu chemistry of this system.     

Copper NQR study of the La 214 system from an aspect of microscopic environment of copper

The nuclear quadrupole resonance (NQR) has been investigated for Cu in La_2–x A _x CuO _y (A=Sr and Ba). Three Cu NQR lines, A, B and C, have been observed, which correspond to three different Cu sites. From the analysis of these NQR intensities, site assignments are possibly as follows. These lines A, B and C are attributed to CuO₆ octahedral, CuO₅ pyramidal and CuO₄ planar sites, respectively. The apical oxygen O(2) is induced to transfer to the interstitial O(3) site between LaO planes when two or more Sr²⁺ ions are located in its neighboring La sites. The excess holes doped into the CuO₂ plane are provided mainly by O(3) as well as the unpaired Sr²⁺ ion.     

NQR investigations of the high-Tc superconductor Ba2YCU3O7

NQR measurements of ^63,65Cu in both the normal and superconducting state are reported for the Cu1 and Cu2 sites in Ba₂YCu₃O₇. An anomalous behaviour in the vicinity and below T_c is observed: after a steep decrease at T_c the quadrupole frequency increases with decreasing temperature.     

Shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cu3O7 and TmBa2Cu4O8

We present a study of shape of the Cu(2) NQR spectra in YBa₂Cu₃O₇, TmBa₂Cum₃O₇, and TmBa₂Cu₄O₈ compounds at temperatures of 4.2–300 K. The results of the quantitative analysis lead us to conclude that the shape of the Cu(2) NQR spectra in all the samples studied can be described in the framework of the “motional narrowing” model, which implies that the Cu(2) nucleus possesses two different NQR frequencies between which it can rapidly jump. The difference in frequencies seems to be related to the charge-stripe correlations in CuO₂ planes resulting in a dynamical modulation of the electric field gradients at the Cu(2) nuclei. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 594–598 (10 November 1997)     

NQR investigations of high-T c superconducting oxides

Nuclear quadrupole resonance (NQR) of⁶³Cu has been performed to study the electronic and magnetic properties of YBa₂Cu₃O_6.1 ceramics, treated in iodine or bromine vapours. An analysis of the NQR shows undistorted CuO₂ planes and the absence of an increase of the oxygen content in chains of Cu(1)-O in halogen treated Y-Ba-Cu-O ceramics.¹³⁹La NQR spin-lattice relaxation measurements in powdered La_2?x CuO_4?y compounds are also reported. The present results indicate that the¹³⁹La nuclear relaxation is dominated by the Cu⁺⁺-Cu⁺⁺ magnetic correlations.     

Ba nuclear resonance in YBa2Cu2Oy

The first observations of NMR and NQR of both isotopes¹³⁵Ba and¹³⁴Ba in isotopically enriched samples of YBa₂Cu₃O_y with oxygen concentrations y=6.0, 6.2, and 7.0 are described. The pure NQR frequencies and asymmetry parameter are in good agreement with theoretical predictions. The temperature dependence of the NQR frequency of Ba for y=7 is qualitatively similar to that for Cu(2) but much stronger. The temperature dependence of the longitudinal and transverse relaxation times opens new questions.     

Magnetic structure of the Sr<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>4</Subscript>Cl<Subscript>2</Subscript> two-subsystem antiferromagnet according to nuclear quadrupole resonance data

The magnetic structure of the Sr₂Cu₃O₄Cl₂ two-subsystem antiferromagnet is studied by the nuclear quadrupole resonance (NQR) method on the ^{63, 65}Cu and ³⁵Cl nuclei. The resonance spectrum above T _N2 = 40 K is determined by the Zeeman splitting of the levels of the ^{63, 65}Cu nuclei of the copper atoms at the Cu1 site with the first-order quadrupole perturbation. The magnetic field on the copper nuclei is equal to 93 kOe. The spectrum below n is significantly different: it includes a low-frequency part, which is associated with the ordering of the second magnetic subsystem Cu2. The splitting of the NQR lines of ³⁵Cl is observed above and below T _N2. This fact indicates the ferromagnetic ordering of the moments of the Cu1 subsystem, which are located along the c axis of the crystal, and makes it possible to determine the direction of the magnetic field on Cu1 copper as (110).     

NMR and NQR studies in high-T c oxides: YBa2Cu3O y (6.0≤y≤6.91)

The NQR and NMR techniques have been utilized to characterize the local oxygen coordination of inequivalent Cu sites and the electronic properties in both the normal and superconducting states of YBa₂Cu₃O_y (6.0<-y≤6.91). The distinct NQR lines associated with the different oxygen-coordinated Cu sites, hence the locally differentiated charged states, have been observed. The degree of charge differentiation at the Cu(2) plane sites was found to be increased with decreasingy from 6.91, which might be related with the decrease ofT _c. An anomalous temperature dependence of Cu nuclear spin-lattice relaxation timeT ₁ has been observed for both the Cu(1) chain and Cu(2) plane sites fory=6.91 and it is discussed in connection with antiferromagnetic spin fluctuations in the normal state.     

Electronic phase separation in TmBa2Cu4O8

The NQR spectra of Cu(2) in the superconductor TmBa₂Cu₄O₈ are studied at temperatures from 300 to 4.2 K. In analyzing the spectra it is assumed that the NQR line of each isotope contains two Gaussian components — narrow (n) and broad (b). It is discovered that the NQR frequencies have a minimum at the temperature T*=150 K. The frequencies of the components of the spectrum are close at temperatures from T* to 4.2 K and differ substantially at temperatures T>T*. Both components are broadened as the temperature decreases, but this broadening occurs especially rapidly at temperatures T<T*. The relative intensity of the narrow component I _n/(I _n+I _b) equals 1/6 for T=225−160 K, increases abruptly at T=T*, and remains constant (1/3) at temperatures T from 125 to 4.2 K. Analysis of the experimental data showed that the anomalous temperature dependences of the Cu(2) NQR spectra could be due to electronic phase separation (stratification) in the CuO₂ planes at temperatures T⩽T*. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 214–219 (10 February 1996)     

Directional behavior of nuclear quadrupole resonance in YBa2Cu3O6

Powder samples of YBa₂Cu₃O₆ were magnetically aligned and the anisotropies in the systems were studied by means of Cu(1) nuclear quadrupole resonance (NQR) in the absence of external magnetic fields. Our room temperature measurements of the NQR lineshapes and the spin–lattice and spin–spin relaxation times as a function of the aligning magnetic field indicate that full microscopic alignment can be achieved by using a magnetic field of about 4.7 T, for which doublet line patterns arising from a hyperfine splitting were observed.     

The two-frequency nuclear quadrupole resonance for explosives detection

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.     

139La and63Cu-NQR of high-T c oxide superconductors

Nuclear quadrupole resonances (NQR) of¹³⁹La in La_2−xM_xCuO₄ (M=Ba, Sr) and⁶³Cu in YBa₂CU₃O₇ have been investigated with substitution of Cu by magnetic impurities. For La-system, the strong enhancement of the nuclear relaxation rate, 1/T ₁ atT _c ^*≈10 K (suggesting the occurrence of magnetic instability with hole-doping), is suppressed by 3D-antiferromagnetism induced by magnetic impurities. In the superconducting region, fluctuations of Cu moments at low temperatures remain extremely fast as at high temperatures. For Y-system, Fe-ions are substituted for both Cu(1) and Cu(2) sites, But Co-ions are preferentially substituted to Cu1 sites. The peaks in the relaxation rate of Cu indicate the appearance of magnetic ordering without destroying superconductivity for the 0.5%-Fe doped sample.     

Modification of SSFP technique for the effective detection of NQR signals

Modification of the steady-state free precession (SSFP) multi-pulse technique for the effective detection of the NQR signals in the presence of a strong coherent noise is proposed. This modification based on the use of additional blocks of the pulses and phase cycling technique enables the suppression of the coherent noise signals such as the magneto-acoustic and piezoelectric signals or the ringing signals from the NQR probe. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of RDX (C₃H₆N₆O₆) are presented and convincingly demonstrate its effectiveness.     

Electronic structure and lattice dynamics of domeykite Cu<Subscript>3</Subscript>As according to nuclear quadrupolar resonance of<Superscript>75</Superscript>As and<Superscript>63,65</Superscript>Cu

The temperature dependences of nuclear quadrupole resonance (NQR) frequencies, the line width and nuclear relaxation of⁷⁵As and^63,65Cu, as well as the electrical resistivity in domeykite Cu₃As are studied in the temperature range of 4.2-300 K. The comparison of the calculated with the measured lattice contribution to the NQR frequencies points at a substantial role played by the conduction electrons in creating the electric field gradient at the nuclei sites. The temperature dependence of the copper and arsenic nuclear spin-lattice relaxation linear at 4.2<T<200 K and that of the electric resistivity (30<T<200 K) prove the metallic character of the conductivity of domeykite. The enhancement of nuclear relaxation, the narrowing of copper and arsenic NQR line widths are considered as arising due to the ionic movement starting beyond 200 K. This movement influences the electric resistivity, most likely due to the inreasing density of states at the Fermi surface.     

NMR experiment on high-T c oxides at Tokyo Metropolitan University

NMR experiments on high-T _c oxides done at Tokyo Metropolitan University are reviewed. The first is⁸⁹Y NMR in YBCO with Y site dilutely substituted by Gd ions. The second isT ₂ ^t-1 of^63,65Cu NQR in YBCO. The third is¹H NMR from probe material coated on YBCO and BSCCO.     

Application of the Wavelet Transform for Detecting Signals of Nuclear Quadrupole Resonance

In the present study, the wavelet transform is used to increase the signal-to-noise ratio of nuclear quadrupole resonance (NQR) signals in the direct pulse method. The efficiency of the wavelet and Fourier transforms used for detecting the NQR signal component is compared. The signal consists of noise, magnetoacoustic and piezoelectric signals, noise from external sources, and NQR signal. Signals from ¹⁴ N nuclei in hexahydro-1,3,5-trinitro-s-triazine C₃H₆N₆O₆ (RDX) are investigated at a temperature of 298 K.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 47–50, January, 2005.     

121,123Sb and 75As NMR and NQR investigation of the tetrahedrite (Cu12Sb4S13) – Tennantite (Cu12As4S13) system and other metal arsenides

This work is motivated by the recent developments in online minerals analysis in the mining and minerals processing industry via nuclear quadrupole resonance (NQR). Here we describe a nuclear magnetic resonance (NMR) and NQR study of the minerals tennantite (Cu₁₂As₄S₁₃) and tetrahedrite (Cu₁₂ Sb₄S₁₃). In the first part NQR lines associated with ⁷⁵As in tennantite and ^121,123Sb isotopes in tetrahedrite are reported. The spectroscopy has been restricted to an ambient temperature studies in accord with typical industrial conditions. The second part of this contribution reports nuclear quadrupole-perturbed NMR findings on further, only partially characterised, metal arsenides. The findings enhance the detection capabilities of NQR based analysers for online measurement applications and may aid to control arsenic and antimony concentrations in metal processing stages.     

Application of the spherical tensor method for Two-Frequency pure NQR of spinI=1 nuclei

The results of a theoretical investigation of two-frequency excitation in pure nuclear quadrupole resonance (NQR) for a spinI=1 nucleus with a nonaxial elecric field gradient are presented. The multipole tensor operator technique is used for the treatment of the one- and two-frequency pulse excitations. The results are applied to the characterization of the two-frequency signal of nitrogen¹⁴N nuclei. The experiments on sodium nitrite, NaNO₂, confirm the presence of additional (two-frequency) echo in the NQR signal. The effect of resonance offsets on two-frequency NQR is also considered.