Cristallographic structure

El sistema (La1-xGdx)1,85Sr0,15CuO4( ) dopado con 1% at. de 57Fe fue estudiado por espectroscopia Mössbauer del 57Fe, susceptibilidad AC y difracción de rayos X. Los estudios a temperatura ambiente nos permitieron interpretar las diferentes especies de Fe (Cu) en función de la vecindad local de oxígeno y las características de las fases T (x=0), T*(x=0,45) y T'(x=1). Las medidas a 4,2 K mostraron que el tipo de orden magnético del Fe (Cu) es influenciado por la geometría local de oxígeno. Se efectuaron mediciones Mössbauer in situ a temperaturas altas en el compuesto Gd1,85Sr0,15CuO4 (fase T') a una presión reducida. La temperatura de Debye obtenida para el Fe en este compuesto es aproximadamente 328 K. El análisis de la variación de las intensidades relativas de los diferentes subespectros permitió monitorar la desorción de los oxígenos cercanos a los iones de Fe.

Ferromagnetic resonance (FMR) study of quasiperiodic Au/Co Fibonacci multilayers revealed that uniform resonance modes related to the bulk Co and interface Au/Co regions of Co layers were excited in all multilayers. Paramagnetic and spin-wave resonance (SWR) modes also were observed into multilayers associated to higher order Fibonacci sequence. The FMR results show that there is no direct correlation between the number of absorption modes and the number of magnetic layers or the Fibonacci generation sequence of the quasiperiodic structure. Analysis of SWR modes revealed an interlayer effective coupling constant higher than that known for conventional Au/Co multilayers.

The authors are indebted to the group of Prof. Dr. A. Conde for sample supplies. This work was partially supported by the CONCYTEC of the Peruvian Government, by CNPq (PCI-program) of the Brazilian Government and by the Latin American Center of Physics. E. Baggio-Saitovitch thanks FAPERJ for the support as Cientista do Nosso Estado.

This work was supported by a grant (No. 013-2013) from the National Council of Science, Technology and Technological Innovation (CONCYTEC/FONDECYT-Peru). Ramos Guivar Juan A. is also grateful to FONDECYT (Grant No. 0218-2014).

This work has been partially supported by the Brazilian agencies CNPq and FAPERJ. H. S. T. thanks to the Peruvian Doctoral Scholarship Program of CIENCIACTIVA (CONCYTEC) for financial support under Grand #218-2014-FONDECYT. J. Q-M and C. V. L. are grateful to CIENCIACTIVA (CONCYTEC) for partial financial support through the Excellence Center Programs. J. Q-M is also grateful to the GEMaC Laboratory, for the hospitality during the preparation of this manuscript. In addition, E. B. S. acknowledges support from FAPERJ through several grants including Emeritus Professor fellow and CNPq for BPA and corresponding grants.

Disordered crystalline Fe50Mn25+xSn25?x alloys, with x =-1.25, 0.0, 2.5, 5.0, 7.5 (close to the full-Heusler alloys), were arc-melted in a high purity argon atmosphere and the molten pellets were individually sealed in quartz tubes also under argon atmosphere. Subsequently, they were annealed at 1173 K for 4 days, being finally quenched in a bath with cold water. Structural and magnetic properties have systematically been studied using X-ray diffraction,57Fe, and119Sn Mössbauer spectroscopies, and magnetization measurements recorded at room temperature. Rietveld refinement of the X-ray diffraction patterns of the annealed samples with x =-1.25 and 0 has revealed the presence of two hexagonal crystallographic phases: (i) a chemically disordered solid solution identified as ??(Fe/Mn)3Sn (majority fraction) and (ii) the ??Fe5Sn3 intermetallic compound (minority fraction). For samples with ...

Fe 50 Ni 50 alloy powder was prepared by milling the 1:1 stoichiometric mixture of Fe and Ni high purity elements using high energy vibrational ball-mill. Final powdered material was obtained directly after 30 h of milling process and the Rietveld analysis of the X-ray diffraction pattern of the sample reveals the presence of two Fe–Ni phases: the disordered ?–(Fe 45 Ni 55 ) alloy, with 91% of total fraction of the material (Fe–Ni solid solution plus grain boundary regions) and the chemically-ordered FeNi phase (9%), with L1 0 tetragonal structure. Average grain sizes of these Fe–Ni phases are respectively 60 nm and 20 nm. Results of extended X-ray absorption fine structure of Ni and Fe as well as 57 Fe Mössbauer spectroscopy also suggest the presence of atomically ordered FeNi phase. Mössbauer data have also shown that both Fe–Ni phases are magnetically ordered at room tempe...