Temperature Dependence of the Cu(2) NQR Line Width in YBa2_2Cu3_3O7−y_{7-y}

Systematic measurements of the $^{63}$Cu(2) NQR line width were performed in underdoped YBa$_2$Cu$_3$O$_{7-y}$ samples over the temperature range 4.2 K $<T<300$ K. It was shown that the copper NQR line width monotonically increases upon lowering temperature in the below-critical region, resembling temperature behavior of the superconducting gap. The observed dependence is explained by the fact that the energy of a condensate of sliding charge-current states of the charge-density-wave type depends on the phase of order parameter. Calculations show that this dependence appears only at $T<T_c$. Quantitative estimates of the line broadening at $T<T_c$ agree with the measurement results.Comment: 4 pages, 2 figure

Electronic structure and indirect spin-spin interactions in bournonite (CuPbSbS3) according to antimony nuclear quadrupole resonance

A complex sulfide CuPbSbS3 (bournonite) has been studied by the nuclear quadrupole resonance on 121,123Sb. The temperature dependences of the spectroscopic and relaxation parameters in the temperature range of 10-295 K have been obtained. The crystallochemical features of the environment of the two non-equivalent Sb positions in the unit cell have been revealed from the nuclear quadrupole resonance spectra. The existence of the lattice vibrations with the frequency ω = 110 cm-1 has been demonstrated on the basis of the temperature dependence of the nuclear quadrupole resonance frequencies. Slow beats have been observed on the decay curve of the spin echo signal. Experimental data have been analyzed in order to reveal the existence of the indirect spin-spin interactions involving Sb atoms. The indirect spin-spin coupling constant has been estimated as J = 2.5 ± 0.5 kHz. © 2013 Pleiades Publishing, Ltd

NMR study of the low temperature magnetic excitations in RBa2(Cu1 - YNiy)3O6 (R = Y, Tm)

Cu(1) NQR, Cu(2) Zero Field NMR and Tm NMR spin-lattice relaxation data have been found quite different in the two AF states of the 123 compounds. In the usual AF-I phase of the pure compounds T1 is short and nearly T-independent at low T. With Ni or Co substitutions in the above by about 2% concentration, the Cu(2) bilayers are ordered ferromagnetically with respect to each other (AF-II phase), which is evidenced by a splitting of the Cu(1) NQR. In this case, T1 -1 is much smaller and exhibits a strong T dependence, which might be associated with a 5 K gap in the magnetic excitation spectrum. We suggest that magnetic defects apparently unavoidable on the Cu(1) sites govern the spin dynamics. While they are frustrated in the "pure samples", they are not in the AF-II phase, which suppresses partly their spin fluctuations

Temperature dependence of the Cu(2) NQR line width in YBa2Cu3O7 - y

Systematic measurements of the 63Cu(2) NQR line width were performed in underdoped YBa2Cu3O7 - y samples over the temperature range 4.2 K < T < 300 K. It was shown that the copper NQR line width monotonically increases with decreasing temperature in the below-critical region, resembling temperature behavior of the superconducting gap. The observed dependence is explained by the fact that the energy of a condensate of sliding charge-current states of the charge-density-wave type depends on the phase of order parameter. Calculations show that this dependence appears only at T < Tc. Quantitative estimates of the line broadening at T < Tc. agree with the measurement results. © 2001 MAIK "Nauka/Interperiodica"

A novel data on Ag5SbS4 and CuPbSbS3 probed by antimony NQR spectroscopy

Investigations of Sb-based chalcogenides, stephanite Ag5SbS 4 and bournonite CuPbSbS 3, have been performed by 121,123Sb nuclear quadrupole resonance (NQR). In stephanite a phase transition at 140 K and internal diffusion motions with an activation energy of 0.29 eV have been experimentally detected. The analysis of experimental results for bournonite revealed two crystal-chemical positions of Sb in the unit cell with distinct local symmetry. The NQR frequencies ν and line-widths Δν data indicate that Sb(A)S3 complex has almost axial symmetry, but Sb(B)S 3 complex is substantially distorted

Crystal field simulation and NMR study of 19F in a EuF3 Van Vleck paramagnet

© 2015 AIP Publishing LLC. The temperature dependence of the nuclear spin-lattice relaxation rate of 19F nuclei is measured for a powder sample of a EuF3 Van Vleck paramagnet, in a broad temperature range (55-300K). The increase in the nuclear relaxation rate observed at T < 100K is caused by fluctuations in the magnetic fields, induced at the fluorine nuclei by the magnetic moments of the europium ions, the lifetime of which is determined by a two-phonon relaxation process with input from the first excited state of the electron shell of Eu3+ ions (Δ1=?370K). The set of crystal field parameters allowing for a satisfactory description of the electron energy spectrum of the Eu3+ ions in the EuF3 crystal, is calculated within the framework of the semi-phenomenological exchange charge model