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J Dolinsek

Publications and source records attributed to J Dolinsek.

At least 19 recordsLinked to original sources

Low temperature charge and orbital textures in La0.875Sr0.125MnO3.

By using nuclear magnetic resonance techniques we show that for T<30 K the La0.875Sr0.125MnO3 compound displays a nonuniform charge distribution, comprised of two interconnected Mn ion subsystems with different spin, orbital, and charge couplings. The NMR results agree very well with the two spin wave stiffness constants observed at small q values in the spin wave dispersion curves [Phys. Rev. B 67, 214430 (2003)]. This picture is probably related to a yet undetermined charge and orbital superstructure occurring in the ferromagnetic insulating state of the La0.875Sr0.125MnO3 compound.

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Orbital domain state and finite size scaling in ferromagnetic insulating manganites.

55Mn and 139La NMR measurements on a high quality single crystal of ferromagnetic (FM) La0.80Ca0.20MnO3 demonstrate the formation of localized Mn(3+,4+) states below 70 K, accompanied by a strong cooling-rate dependent increase of certain FM neutron Bragg peaks. (55,139)(1/T(1)) spin-lattice and (139)(1/T(2)) spin-spin relaxation rates are strongly enhanced on approaching this temperature from below, signaling a genuine phase transition at T(tr) approximately 70 K. The disappearance of the FM metallic signal by applying a weak external magnetic field, the different NMR radio-frequency enhancement of the FM metallic and insulating states, and the observed finite size scaling of T(tr) with Ca (hole) doping, as observed in powder La(1-x)CaxMnO3 samples, are suggestive of freezing into an inhomogeneous FM insulating and orbitally ordered state embodying "metallic" hole-rich walls.

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Dynamics of the pinned modulation wave in incommensurate bis (4-chlorophenyl) sulfone (BCPS).

We show that both the anomalously huge resonance-frequency dependence of the (35)Cl nuclear quadrupole resonance (NQR) spin-lattice relaxation time in BCPS, reported here for the first time, and its anomalous temperature dependence can be explained by large-scale fluctuations of the pinned modulation wave instead of small-scale fluctuations (phasons and amplitudons). The results were obtained by measuring the laboratory (T(1Q)) and rotating frame (T(1Q,rho)) (35)Cl relaxation times. This is the first time that an effective resonance frequency dependence of the spin-lattice relaxation rate was measured in pure NQR.

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Modeling the static fringe field of superconducting magnets.

The resonance frequency-space and the frequency gradient-space relations are evaluated analytically for the static fringe magnetic field of superconducting magnets used in the NMR diffusion measurements. The model takes into account the actual design of the high-homogeneity magnet coil system that consists of the main coil and the cryoshim coils and enables a precise calibration of the on-axis magnetic field gradient and the resonance frequency inside and outside of the superconducting coil.

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Ultrasonographic assessment of celiac disease in children: comparison with antiendomysium antibodies and histology.

UNLABELLED: Several attempts have been made to identify accurate screening tests for celiac disease (CD) with the aim to reduce the need for biopsy or obtaining appropriate selection criteria prior to intestinal biopsy. In this context we evaluated the usefulness of screening for endomysial antibodies (EMA) in the diagnosis of CD in children in comparison with CD-related changes detected by ultrasound (US) or biopsy. PATIENTS: We studied 35 children (1-15 years, 22 girls and 13 boys, mean age 8 years) with untreated CD (N = 15), treated CD (N = 10) and controls (N = 10), undergoing small bowel biopsy as a diagnostic procedure. METHODS: US of the small bowel was performed prior to mucosa biopsy using a 4- or 7-MHz transducer of a computed sonography device. The thickness of the intestinal wall and small bowel motility were recorded. Simultaneously, all children had serum routinely sampled for IgA EMA. RESULTS: All controls had histologically normal small bowel mucosa, US showed a small bowel wall thickness of 1 mm with normal motility in 9 children and non-specific wall changes in 1 child. EMA was weakly positive in 1 of these, and negative in all other controls. Of 15 children with untreated CD, severe enteropathy and strongly positive EMA were found in 10 cases; in 5 children moderate enteropathy and positive EMA were detected. Severe US changes were found in all of these children (1.6 mm thickness of the intestinal wall, hyperperistalsis and abundant fluid in the bowel). Mild enteropathy was found in 10 children with treated CD (3 months of a gluten-free diet). EMA was positive in 2 children and weakly positive in 8. Non-specific US changes were found in 6 children. In conclusion, our results indicate that US provides valuable information on small-bowel wall structure and can help in decision making on the necessity of small bowel biopsy. The present study confirms a stronger correlation between EMA and CD than between US and CD.

Adolescent↗

55Mn NMR investigation of electronic phase separation in La1-xCaxMnO3 for 0.2 < or = x < or = 0.5.

55Mn NMR line shape measurements in La1-xCaxMnO3 for 0.20< or =x< or =0.50 provide experimental evidence about the existence of two distinct regions in the T-x magnetic phase diagram, where the homogeneous ferromagnetic (FM) metallic state is separated into FM metallic and FM insulating regions. These results are in agreement with recent theoretical predictions, which reveal a novel electronic phase separation in two FM states, providing orbital ordering and Jahn-Teller phonons are taken into consideration.

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Phonon-assisted spin diffusion in solids

The spin flip-flop transition rate is calculated for the case of spectral spin diffusion within a system of dipolarly coupled spins in a solid where the lattice vibrations are present. Long-wavelength acoustic phonons time-modulate the interspin distance r(ij) and enhance the transition rate via the change of the 1/r(3)(ij) term in the coupling dipolar Hamiltonian. The phonon-assisted spin diffusion rate is calculated by the golden rule in the Debye approximation of the phonon density of states. The coupling of the spins to the phonons introduces temperature dependence into the transition rate, in contrast to the spin diffusion in a rigid lattice, where the rate is temperature-independent. The direct (one-phonon absorption or emission) processes introduce a linear temperature dependence into the rate at temperatures not too close to T = 0. Two-phonon processes introduce a more complicated temperature dependence that again becomes simple analytical for temperatures higher than the Debye temperature, where the rate is proportional to T(2), and in the limit T --> 0, where the rate varies as T(7). Raman processes (one-phonon absorption and another phonon emission) dominate by far the phonon-assisted spin flip-flop transitions. Copyright 2000 Academic Press.

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