Inhomogeneity of the intrinsic magnetic field in superconducting YBa 2Cu3OX compounds as revealed by a rare-earth EPR probe

X-band electron paramagnetic resonance experiments on doped Er 3+ and Yb3+ ions in YBa2Cu3O X (6<X<7) compounds with different oxygen contents in a wide temperature range (4-120 K) have been performed. In the superconducting species at temperatures significantly below TC, strong dependences of the linewidth and resonance line position on the sweep direction of the applied magnetic field are revealed. The possible origins of the observed hysteresis are analysed. The applicability of the presented EPR approach to extract information about the dynamics of the flux-line lattice and critical state parameters (critical current density, JC, magnetic penetration depth, λ, and characteristic spatial scale of the inhomogeneity) is discussed. © 2005 IOP Publishing Ltd

Electron spin-lattice relaxation in polyacetylene at low temperatures

Temperature dependences of electron spin-lattice relaxation times for cis- and trans-polyacetylene are measured at 2-40 K. A model of relaxation in trans-polyacetylene is suggested where the relaxation proceeds via spin diffusion to fast relaxing centers (a pair of close spins, one of which is highly mobile). Theoretical calculations of relaxation rates for both configurations of polyacetylene are presented, which give qualitative and quantitative description of measured relaxation times

Electronic spin lattice relaxation in oligoarylenes in the naphthalene-benzene copolymer

Spin-lattice relaxation of paramagnetic centres in the naphthalene-benzene copolymer and in the products of its pyrolysis has been investigated in some detail at various temperatures. It appears from the experimental results that two-step Orbach-Aminov type relaxation processes take place in the pyrolyzed samples, and may be accounted for satisfactorily through the relaxation model in terms of exchange-bound clusters. The results of the relaxation measurements are compared with the data obtained by infrared, and by elemental analysis and X-ray studies. © 1986

Electron Spin-Lattice Relaxation of Er3+ ions in Er0.01Y0.99Ba2Cu3Ox

The temperature dependence of the electron spin-lattice relaxation SLR was studied in Er0.01Y0.99Ba2Cu3Ox compounds. The data derived from the electron spin resonance ESR and SLR measurements were compared to those from inelastic neutron scattering studies. SLR of Er3+ ions in the temperature range from 20 K to 65 K can be explained by the resonant phonon relaxation process with the involvement of the lowest excited crystalline-electric-field electronic states of Er3+. These results are consistent with a local phase separation effects. Possible mechanisms of the ESR line broadening at lower temperatures are discussed. Keywords: YBCO; EPR; ESR; Electron spin-lattice relaxation time, T ; Crystalline-electric-fieldComment: 6 pages, 4 figure

Effect of Mo3+ ions on Nd3+ spin-lattice relaxation in Y3Al5O12

The content of Mo3+ ions in YAG:Nd garnet samples prepared by different technologies has been studied, and the spin-lattice relaxation rate of these ions at temperatures of 4-5 K measured. It is concluded is drawn that Mo3+ ions can play the part of rapidly relaxing centers mediating the Nd3+ spin-lattice relaxation at liquid-helium temperatures. This may account for a number of features in the spin-lattice relaxation of rare-earth ions in garnets, observed earlier at low temperatures. © 1998 American Institute of Physics

The electron spin-lattice relaxation in pyrolyzed poly-2-methyl-5-ethinylpyridine

The temperature and field dependences of the rate of electron spin-lattice relaxation (ESLR) have been studied on poly-2-methyl-5-ethinyl pyridine (PMEP), which had been pyrolyzed at various temperatures. The experimental results are interpreted from the aspect of the theoretical calculations predicting the diversity of these dependences in the case of linear-and laminar-structure polymers. The results of the evaluations are compared with those of elemental analysis and IR-spectroscopy. © 1982

Inhomogeneity of the intrinsic magnetic field in superconducting YBa2Cu3OX compounds as revealed by rare-earth EPR-probe

X-band electron paramagnetic resonance on doped Er3+ and Yb3+ ions in Y0.99(Yb,Er)0.01Ba2Cu3OX compounds with different oxygen contents in the wide temperature range (4-120)K have been made. In the superconducting species, the strong dependencies of the linewidth and resonance line position from the sweep direction of the applied magnetic field are revealed at the temperatures significantly below TC. The possible origins of the observed hysteresis are analyzed. Applicability of the presented EPR approach to extract information about the dynamics of the flux-line lattice and critical state parameters (critical current density, magnetic penetration depth, and characteristic spatial scale of the inhomogeneity) is discussedComment: 17 pages, 5 Figures. Renewed versio

Identification of the La6F37 cubooctahedral clusters in mixed crystals (BaF2)1 - X (LaF3) x by the electron paramagnetic resonance method

The electron paramagnetic resonance (EPR) spectra of mixed crystals (BaF2)1 - x (LaF3) x (x = 0, 0.001, 0.002, 0.005, 0.010, 0.020) doped with Ce3+ ions (0.1%) are investigated at a frequency v ≈ 9.5 GHz in magnetic fields up to 1.45 T at temperatures T = 10 and 15 K. The EPR spectrum of "pure" barium fluoride BaF2 (x = 0) is characterized by a single Ce 3+-F- center with tetragonal symmetry (i.e., the O center with g || = 2.601 and g ⊥ = 1.555). For a lanthanum trifluoride concentration x 0, the spectrum exhibits new lines due to the presence of the clusters containing Ce3+ and La3+ ions. The intensity of EPR signals from the O centers decreases rapidly as the lanthanum trifluoride concentration x increases. The lines attributed to a paramagnetic center with tetragonal symmetry and strongly anisotropic g factors (i.e., the K center with g || = 0.725 and g ⊥ = 2.52) are separated in the complex EPR spectrum with the use of the angular dependence of the EPR signal intensity measured for the samples with x > 0.002. This center is identified as a cubooctahedral cluster of the La 6F37 type in which one of the La3+ ions is replaced by the Ce3+ ion. © 2007 Pleiades Publishing, Ltd

Field dependence of spin-lattice relaxation of Nd3+ ions in y3Al5O12 crystals

Our studies involve measuring spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets over the temperature range 4-50 K at 9.25 and 36.4 GHz for different orientations of the external magnetic field in relation to the crystallographic axes. The temperature dependence of the relaxation rate is described by T1 -1=ATn + b exp(-ΔAT), where n varies from sample to sample, with n=1 for "perfect" samples (i.e., with the longest relaxation times). Here A is approximately 130 cm-1, which is the energy of the excited Kramers doublet of the neodymium ion closest to the ground state, and this makes it possible to interpret the second term in T1 -1 as the contribution of two-stage relaxation proceeding through the intermediate level Δ. A strong field dependence of these processes has been discovered: when the frequency was increased fourfold, the relaxation rate increased by a factor of 10. The effect is a specific manifestation of the degeneracy of the excited level, breaking of the symmetry of the crystalline field due to lattice defects, and the prevalence of deformations of a certain type in the spin-lattice interaction. ©1997 American Institute of Physics

EPR of rare-earth ion clusters in mixed crystals Ba1-xLa xF2+x doped with Yb3+ ion

Electron paramagnetic resonance (EPR) spectra of Yb3+ ions in the mixed crystals (BaF2)1-xX (LaF3) x with x ≈ 0.01 have been investigated by the electron spin echo method at a frequency of 94.9 GHz and compared with the spectra obtained by the continuous-wave EPR at a frequency of 9.5 GHz. Some spectral lines were identified within the framework of the simple cluster model proposed in our previous work (L. K. Aminov, R. Yu. Abdulsabirov, M. R. Gafurov, S. L. Korableva, I. N. Kurkin, S. P. Kurzin, R. M. Rakhmatullin, A. G. Ziganshin: Appl. Magn. Reson. 28, 41-53, 2005). Clusters consist of trigonal dipoles La-F and Yb-F (a rare-earth ion with a charge compensator) and are formed beginning with small concentrations x ≈ 0.001. The lines identified in the present work were attributed to the clusters with configurations Yb-F-La-F and La-F-Yb-F-La-F. © Springer-Verlag 2005