Spin-orbit induced mixed-spin ground state in RRNiO3_3 perovskites probed by XAS: new insight into the metal to insulator transition

We report on a Ni L$_{2,3}$ edges x-ray absorption spectroscopy (XAS) study in $R$NiO$_3$ perovskites. These compounds exhibit a metal to insulator ($MI$) transition as temperature decreases. The L$_{3}$ edge presents a clear splitting in the insulating state, associated to a less hybridized ground state. Using charge transfer multiplet calculations, we establish the importance of the crystal field and 3d spin-orbit coupling to create a mixed-spin ground state. We explain the $MI$ transition in $R$NiO$_3$ perovskites in terms of modifications in the Ni$^{3+}$ crystal field splitting that induces a spin transition from an essentially low-spin (LS) to a mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200

Unprecedented magnetoresistance in Cd-substituted Tl2Mn2O7 pyrochlores

3 pages, 3 figures.Moderate pressure techniques (P = 20 kbar) have been used to prepare Tl2–xCdxMn2O7 (0x0.4) pyrochlore-like materials. The x = 0.2 compound has been characterized by neutron powder diffraction, magnetic, magnetotransport, and Hall measurements. This material is ferromagnetic below TC = 110 K. Both electrical resistance and magnetoresistance (MR) are enhanced with respect to stoichiometric Tl2Mn2O7, due to the drastic reduction in the number of carriers (electrons) induced by hole doping. MR(0.5 T) is higher than 106% at 120 K, and MR(9 T) is 30% at room temperature. We show that hole doped derivatives of Tl2Mn2O7 are promising candidates in which to search for large bulk magnetoresistance.The author are grateful for the financial support of CICyT (Project Nos. PB97-1181 and MAT99-1045).Peer reviewe

«ESTUDIO DEL CONTENIDO EN ACIDO FITICO DURANTE EL PROCESO INDUSTRIAL DE ELABORACION DE GALLETAS»

An assessment on the phytic acid contents during the baking process of biscuits has been carried out. The analytical method used is one formerly proposed by us, based on an indirect complexometry with Fe(III). No modification of the phytic acid contents has been noticed.Se ha efectuado un estudio del contenido en ácido fítido durante el proceso de fabricación de galletas empleando el método analítico propuesto por nosotros, basado en una complexometría indirecta con Fe(III) y se ha confirmado que no hay alteración alguna durante todo el proceso

R-symmetric Gauge Mediation and the MRSSM

This is an invited summary of a seminar talk given at various institutions in the United States and Canada. After a brief introduction, a review of the minimal R-symmetric supersymmetric standard model is given, and the benefits to the flavor sector are discussed. R-symmetric gauge mediation is an attempt to realize this model using metastable supersymmetry breaking techniques. Sample low energy spectra are presented and tuning is discussed. Various other phenomenological results are summarized.Comment: 14 pages, invited Brief Review, submitted to Modern Physics Letters A; v2: replaced Figure 1, updated acknowledgments, fixed typo

Estudio del contenido en ácido fitico durante el proceso industrial de elaboración de galletas

Agradecemos sinceramente a D. Antonio García García, Gerente de «Galletas Cuétara», así como al personal de la fábrica las facilidades y atenciones que nos han prestado en la realización de este trabajo.Se ha efectuado un estudio del contenido en ácido fítido durante el proceso de fabricación de galletas empleando el método analítico propuesto por nosotros, basado en una complexometría indirecta con Fe(III) y se ha confirmado que no hay alteración alguna durante todo el proceso.An assessment on the phytic acid contents during the baking process of biscuits has been carried out. The analytical method used is one formerly proposed by us, based on an indirect complexometry with Fe(III). No modification of the phytic acid contents has been noticed

Raman phonons as a probe of disorder, fluctuations and local structure in doped and undoped orthorhombic and rhombohedral manganites

We present a rationalization of the Raman spectra of orthorhombic and rhombohedral, stoichiometric and doped, manganese perovskites. In particular we study RMnO3 (R= La, Pr, Nd, Tb, Ho, Er, Y and Ca) and the different phases of Ca or Sr doped RMnO3 compounds as well as cation deficient RMnO3. The spectra of manganites can be understood as combinations of two kinds of spectra corresponding to two structural configurations of MnO6 octahedra and independently of the average structure obtained by diffraction techniques. The main peaks of compounds with regular MnO6 octahedra, as CaMnO3, highly Ca doped LaMnO3 or the metallic phases of Ca or Sr doped LaMnO3, are bending and tilt MnO6 octahedra modes which correlate to R-O(1) bonds and Mn-O-Mn angles respectively. In low and optimally doped manganites, the intensity and width of the broad bands are related to the amplitude of the dynamic fluctuations produced by polaron hopping in the paramagnetic insulating regime. The activation energy, which is proportional to the polaron binding energy, is the measure of this amplitude. This study permits to detect and confirm the coexistence, in several compounds, of a paramagnetic matrix with lattice polaron together with regions without dynamic or static octahedron distortions, identical to the ferromagnetic metallic phase. We show that Raman spectroscopy is an excellent tool to obtain information on the local structure of the different micro or macro-phases present simultaneously in many manganites.Comment: Submitted to PR