On the hyperfine interaction in rare-earth Van Vleck paramagnets at high magnetic fields

An influence of high magnetic fields on hyperfine interaction in the rare-earth ions with non-magnetic ground state (Van Vleck ions) is theoretically investigated for the case of $Tm^{3+}$ ion in axial symmetrical crystal electric field (ethylsulphate crystal). It is shown that magnetic-field induced distortions of $4f$-electron shell lead to essential changes in hyperfine magnetic field at the nucleus. The proposed theoretical model is in agreement with recent experimental data.Comment: 4 pages, no figures, submitted to J. Phys. : Cond. Mat

A geometric interpretation of the spectral parameter for surfaces of constant mean curvature

Considering the kinematics of the moving frame associated with a constant mean curvature surface immersed in S^3 we derive a linear problem with the spectral parameter corresponding to elliptic sinh-Gordon equation. The spectral parameter is related to the radius R of the sphere S^3. The application of the Sym formula to this linear problem yields constant mean curvature surfaces in E^3. Independently, we show that the Sym formula itself can be derived by an appropriate limiting process R -> infinity.Comment: 12 page

Rare-earth ion clusters in doped crystals with fluorite structure

In BaF2 crystals doped with paramagnetic Yb3+ ions, at concentrations higher than 0.01 at %, an EPR line was observed corresponding to a linear cluster Yb-F-Yb-F oriented along a threefold axis. © 2009 Pleiades Publishing, Ltd

Concentration dependence of EPR spectra in mixed (BaF2)1 - x(CeF3)x crystals

In the EPR spectra of the (BaF2)1 - x(CeF3)x system, additional lines appear as the concentration x in the mixture increases from 10-3 to 10-2, some of which correspond to tetragonal centers with g{norm of matrix} = 0. 725 and g⊥ = 2. 52. These lines are similar to those detected previously in mixed (BaF2)1 - x - y(CeF3)x(LaF3)y systems with a low cerium concentration (x ≈ 10-3) and in the CaF2: Ce3+ crystal grown with added Na+ ions. © 2013 Pleiades Publishing, Ltd

Calculation of spin-lattice relaxation times

A general expression is found for the probability for a direct (single-phonon) relaxation transition for arbitrary symmetry of the surroundings of a paramagnetic ion having an effective spin of S = 1/2. The expression is compared with experiment for the case of tetragonal symmetry. Since certain approximations frequently used in the calculations are not used here, a markedly improved agreement is found with the experimental relaxation times. © 1972 Consultants Bureau

Temperature dependence of the EPR linewidth of Yb3+ - ions in Y0.99Yb0.01Ba2Cu3OX compounds: Evidence for an anomaly near TC

Electron paramagnetic resonance experiments on doped Yb3+ ions in YBaCuO compounds with different oxygen contents have been made. We have observed the strong temperature dependence of the EPR linewidth in the all investigated samples caused by the Raman processes of spin-lattice relaxation. The spin-lattice relaxation rate anomaly revealed near TC in the superconducting species can be assigned to the phonon density spectrum changesComment: 10 pages, 4 figures Renewed versio

Some peculiarities of spin-lattice relaxation of impurity rare-earth ions in crystals, caused by the structure defects

The spin-lattice relaxation times for Nd3+ ions in yttrium-aluminum garnets (YAG) and for Yb3+ ions in CaF2 in the low-temperature range have been measured. For the first system the temperature dependence of the relaxation rate is determined to a great extent by the method of sample preparation. For samples grown by the method of the horizontally oriented crystallization the dependence is described as T1 -1 = ATn, n ≅ 4.7, which is an evidence of an influence of local structure disordering on the relaxation. The temperature dependence of the relaxation rate in CaF2:Yb is also "anomalous": T1 -1 = AT3.3. The results are compared with the previous data on the relaxation in similar systems, and with other cases of observation of "anomalous" temperature dependences. Different manifestations of the local crystal defects in spin-lattice relaxation are discussed. © Springer-Verlag 1998 Printed in Austria

Classical and quantum dynamics of confined test particles in brane gravity

A model is constructed for the confinement of test particles moving on a brane. Within the classical framework of this theory, confining a test particle to the brane eliminates the effects of extra dimensions, rendering them undetectable. However, in the quantized version of the theory, the effects of the gauge fields and extrinsic curvature are pronounced and this might provide a hint for detecting them. As a consequence of confinement the mass of the test particle is shown to be quantized. The condition of stability against small perturbations along extra dimensions is also studied and its relation to dark matter is discussed.Comment: 15 pages, no figures, extended, references adde

Pseudospherical surfaces on time scales: a geometric definition and the spectral approach

We define and discuss the notion of pseudospherical surfaces in asymptotic coordinates on time scales. Thus we extend well known notions of discrete pseudospherical surfaces and smooth pseudosperical surfaces on more exotic domains (e.g, the Cantor set). In particular, we present a new expression for the discrete Gaussian curvature which turns out to be valid for asymptotic nets on any time scale. We show that asymptotic Chebyshev nets on an arbitrary time scale have constant negative Gaussian curvature. We present also the quaternion-valued spectral problem (the Lax pair) and the Darboux-Backlund transformation for pseudospherical surfaces (in asymptotic coordinates) on arbitrary time scales.Comment: 20 page

Temperature dependence of the EPR linewidth of Yb3+ ions in Y0.99Yb0.01Ba2Cu3OX (6 ≤ X ≤ 7) compounds: Evidence for an anomaly near the superconducting transition

Electron paramagnetic resonance experiments on doped Yb3+ ions in Y0.99Yb0.01Ba2Cu3OX (6 ≤ X ≤ 7) compounds with different oxygen contents have been made. We have observed a strong temperature dependence of the EPR linewidth in all the investigated samples caused by the Raman processes of spin-lattice relaxation. The spin-lattice relaxation rate anomaly revealed near TC in the superconducting species can be assigned to the phonon density spectrum changes. © 2005 IOP Publishing Ltd