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http://hdl.handle.net/10261/46
20150729T22:07:59Z

Origin of incommensurate satellite reflections on TbMnO3 by resonant xray scattering
http://hdl.handle.net/10261/117730
Título : Origin of incommensurate satellite reflections on TbMnO3 by resonant xray scattering
Autor : Cuartero, Vera; García, Joaquín; Subías, G.; HerreroMartín, Javier; Blasco, Javier; Natoli, Calogero R.
Resumen: We have performed a deep spectroscopic study of incommensurate satellite reflections (h, k, l) ± (0,0.278, 0) on a TbMnO3 single crystal in order to shed light on its physical origin. Resonant xray scattering experiments at the Mn Kedge and Tb L3edge have been performed at different temperatures and azimuthal angles, analyzing the outgoing light polarization. Our experimental results agree with a magnetic origin for A and Ctype reflections, while F and Gtype have the hallmarks of anisotropic tensor susceptibility (ATS) reflections, so that they come purely from the structural modulation.
Descripción : Trabajo presentado a la 15th International Conference on Xray Absorption Fine Structure (XAFS15), celebrada del 22 al 28 de julio de 2012 en Pekín (China). Licencia Creative Commons Reconocimiento 3.0
20150708T10:48:37Z

Lanthanide contraction within a series of asymmetric dinuclear [Ln 2] complexes
http://hdl.handle.net/10261/117669
Título : Lanthanide contraction within a series of asymmetric dinuclear [Ln 2] complexes
Autor : Aguilà, D.; Barrios, L. A.; AliagaAlcalde, N.; Teat, Simon J.; Roubeau, Olivier; Luis, Fernando; Aromí, Guillem
Resumen: A complete isostructural series of dinuclear asymmetric lanthanide complexes has been synthesized by using the ligand 6[3oxo3(2hydroxyphenyl) propionyl]pyridine2carboxylic acid (H3L). All complexes have the formula [Ln2(HL)2(H2L)(NO3)(py) (H2O)] (Ln=La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14), Y (15); py=pyridine). Complexes of La to Yb and Y have been crystallographically characterized to reveal that the two metal ions are encapsulated within two distinct coordination environments of differing size. Whereas one site maintains the coordination number (nine) through the whole series, the other one increases from nine to ten owing to a change in the coordination mode of an NO3  ligand. This series offers a unique opportunity to study in detail the lanthanide contraction within complexes of more than one metal. This analysis shows that various representative parameters proportional to this contraction follow a quadratic decay as a function of the number n of f electrons. Slater's model for the atomic radii has been used to extract, from these decays, the shielding constant of 4f electrons. The average of O×××O distances within the coordination polyhedra shared by both metals and of the Ln×××Ln separations follow also a quadratic decay, therefore showing that such dependence holds also for parameters that receive the contribution of two lanthanide ions simultaneously. The magnetic behavior has been studied for all nondiamagnetic complexes. It reveals the effect of the spinorbit coupling and a weak antiferromagnetic interaction between both metals. Photoluminescent studies of all the complexes in the series reveal a single broad emission band in the visible region, which is related to the coordinated ligand. On the other hand, the Nd, Er, and Yb complexes show features in the nearIR region due to metalbased transitions. Copyright © 2013 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim.
20150707T11:09:45Z

Ground state and the metalinsulator transition in (Pr1yYy)1xCaxCoO3 (0.45 ≤ x ≤ 0.55) cobaltites
http://hdl.handle.net/10261/117613
Título : Ground state and the metalinsulator transition in (Pr1yYy)1xCaxCoO3 (0.45 ≤ x ≤ 0.55) cobaltites
Autor : BarónGonzález, A. J.; GarcíaMuñoz, J. L.; HerreroMartín, Javier; Frontera Beccaria, Carlos; Subías, G.; Blasco, Javier
Resumen: Pr0.5Ca0.5CoO3 exhibits a nonconventional metalinsulator transition (MIT) in which the insulating state is due toa volume contraction (∼2%) and electron transfer from Pr to Co sites. Pr1xCaxCoO3cobaltites with Ca doping around x ∼ 0.5 (0.45 ≤ x ≤ 0.55) have been investigated. Different ground states and phase transitions are reported in samples at both sides of the halfdoped composition. The relevance of the Pr/Ca ratio around halfdoping and the amplitude of the changes observed at the MIT are analyzed. Besides the expected variation in the transition temperature, we report an enhanced Pr3+/Pr4+ transformation at the MIT in Pr0.45Y0.05Ca0.50CoO3[0.25(5) e/Pr ion and T MI = 120 K] with respect to Pr0.5Ca0.5CoO3[0.15(5) e/ Pr ion and T MI = 75 K]. © 2013 The Korean Physical Society.
20150706T11:29:45Z

Determination of incommensurate lattice modulations in La0.4Sr1.6MnO4 by resonant rray scattering
http://hdl.handle.net/10261/117533
Título : Determination of incommensurate lattice modulations in La0.4Sr1.6MnO4 by resonant rray scattering
Autor : García, Joaquín; HerreroMartín, Javier; Subías, G.; Blasco, Javier; Sánchez, María Concepción
Resumen: Superlattice reflections, which appear below the semiconductorinsulator phase transition temperature in La0.4Sr1.6MnO4, have been investigated by Resonant Xray Scattering. We have observed two types of resonant reflections with modulation wave vectors qh±epsilon = (h±epsilon, h±epsilon, 0) and qh±2epsilon = (h±2epsilon, h±2epsilon, 0) (h=integer, epsilon=0.2) in the I4/mmm setting. The energy dependence across the Mn Kedge, together with the azimuthal angle, polarization and temperature evolution have shown that reflections with 2epsilon periodicity only appear in the σσ' channel, involving resonant and nonresonant scattering. On the other hand, reflections with epsilon periodicity exclusively appear in the σπ' channel on resonance and the scattered intensity follows a πperiodicity with the azimuthal angle. We demonstrate that this different behaviour discards any possible Mn3+/Mn4+like bimodal stripe ordering but it can be easily explained as due to oxygen displacements sinusoidal modulated along and perpendicular to the tetragonal [1, 1, 0] direction.
Descripción : Trabajo presentado a la 15th International Conference on Xray Absorption Fine Structure (XAFS15) 22–28 July 2012, Beijing, China. Under the Creative Commons AttributionUnported (CCBY) 3.0 license.
20150703T10:45:26Z