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

Study of the crystal field in CeF<inf>3</inf> and CeF<inf>3</inf>:Pr³⁺

© Kazan Federal University (KFU).The crystal field analysis based on calculations in the framework of the semi phenomenological exchange charge model was carried out. The set of crystal field parameters for Ce3+ and Pr3+ ions in the matrix CeF3 related to the crystallographic system of coordinates has been obtained and used to reproduce satisfactory the crystal field energies of Ce3+ and Pr3+ ions

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"

Application of the LASSO algorithm for fitting the multiexponential data of the NMR relaxometry

© 2018 Institute of Physics Publishing. All rights reserved. The problem of time series fitting by the sum of several exponentials with different decay parameters often arises analyzing the data of a physical experiment. In particular, such a problem arises determining the nuclear transverse relaxation times from the spin-echo decay NMR data. Mathematically, the problem can be formulated as a solution of the Fredholm integral equation of the first kind with an exponential kernel, or an equivalent system of linear equations. To solve this equation, various regularization methods are used, based on the L2-norm in most cases. We report the application of the L1-regularization for the problem, using the LASSO algorithm. A comparison was made between the results of L1- and L2-regularization on model time series, which were the sum of several exponential decays with noise. Also the L1- and L2-regularization were applied to analyze the 1H NMR experimental data of the spin-echo decays of n-hexane adsorbed in the porous volume of aluminium poor MFI-type zeolites known as ZSM-5. It was found out that the L1-regularization is effective method for determination of the transverse relaxation times from NMR data

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

Copper valence, structural separation and lattice dynamics in tennantite (fahlore): NMR, NQR and SQUID studies

Electronic and magnetic properties of tennantite subfamily of tetrahedrite-group minerals have been studied by copper nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR) and SQUID magnetometry methods. The temperature dependences of copper NQR frequencies and line-width, nuclear spin-lattice relaxation rate T1 -1 and nuclear spin-echo decay rate T2 -1 in tennantite samples in the temperature range 4.2-210 K is evidence of the presence of field fluctuations caused by electronic spins hopping between copper CuS3 positions via S2 bridging atom. The analysis of copper NQR data at low temperatures points to the magnetic phase transition near 65 K. The magnetic susceptibility in the range 2-300 K shows a Curie-Weiss behavior, which is mainly determined by Fe2+ paramagnetic substituting ions. © Springer-Verlag 2007

Revised Measurements and Interpretation of Magnetic Properties of Oriented CeF <inf>3</inf> Single Crystals

© 2016, Springer Science+Business Media New York.We report the magnetic susceptibility and magnetization of the single-crystal CeF3 precisely measured in external magnetic field-directed B| | c and B⊥c in wide ranges of temperatures from 1.8 to 300 K and magnetic field strength of 0–40 kG. Magnetic susceptibility, magnetization, and Ce3 + Stark energies of CeF3 have been calculated in the framework of the crystal field theory; good agreement with the experimental data has been achieved in the whole range of temperatures and magnetic fields without taking into account the mixed-valent Ce3 +-Ce4 + behavior or super-exchange interaction of cerium ions that have been proposed before. Anomalous behavior of the magnetic susceptibility near T ∼ 50 K is naturally explained in the crystal field model

Revised Measurements and Interpretation of Magnetic Properties of Oriented CeF3 Single Crystals

© 2016 Springer Science+Business Media New YorkWe report the magnetic susceptibility and magnetization of the single-crystal CeF(Formula presented.) precisely measured in external magnetic field-directed B(Formula presented.)c and B(Formula presented.)c in wide ranges of temperatures from 1.8 to 300 K and magnetic field strength of 0–40 kG. Magnetic susceptibility, magnetization, and Ce(Formula presented.) Stark energies of CeF(Formula presented.) have been calculated in the framework of the crystal field theory; good agreement with the experimental data has been achieved in the whole range of temperatures and magnetic fields without taking into account the mixed-valent Ce(Formula presented.)-Ce(Formula presented.) behavior or super-exchange interaction of cerium ions that have been proposed before. Anomalous behavior of the magnetic susceptibility near T (Formula presented.) 50 K is naturally explained in the crystal field model

Dynamics and distribution of doped holes in the CuO2 plane of slightly doped antiferromagnetic YBa2(Cu1-zLiz)3O6+x (x < 0.1) studied by Cu(1) NQR

Incidence of doped holes in the CuO2 plane on the AF state was studied by Cu(1) nuclear quadrupole resonance (NQR) in slightly doped YBa2(Cu1-zLiz)3O6+x compounds. Inhomogeneous distribution of doped holes in the plane was detected in the low temperature measurements of transverse (1/T2) and longitudinal (1/T1) relaxation rates. We establish that at lower T the holes motion slows down and we estimate that the holes localize finally in restricted regions (~3 lattice constants) in the Coulomb potential of the Li+ ions. Also we compared the hole behavior in slightly doped YBa2(Cu1-zLiz)3O6+x samples with that in slightly doped Y1-yCayBa2Cu3O6. A stronger trapping potential of the in-plane Li+ impurities was concluded as compared to slightly doped Y1-yCayBa2Cu3O6 compound with out-of-plane Ca2+ impurities. © Pleiades Publishing, Inc., 2010