The temperature dependent transport coefficients are theoretically examined in different phases ofthe Al-Cu­ Fe system. In the present work we focus on the conductivity and the thermoelectric power. The spectral resistivity is modeled by means of Lorentzian functions, in agreement with our ab-initio results (linear muffm-tin orbital basis and Kubo-Greenwood formula). This model considers the most important information of the ab-initio results in order to explain consistently the transport coefficients mentioned above. The numerical results shown in this work are in good agreement with the experimental ones.

In the present work we perform the systematic study, employing X-ray diffraction and Mössbauer spectrometry, of the variation of the structural and hyperfine parameters during the milling process of the icosahedral Al64Cu23Fe13 quasicrystal. For this purpose, the samples were prepared by arc-furnace technique followed by heat treatment. Then, the samples were nanoestructured in a high energy ball milling equipment during 5, 10, 15, 20, 45, 50 and 60 hours. The X-ray diffraction patterns show the stability of the nanoestructured samples. Furthermore, the Mössbauer spectra indicate the increase of the Fe-sites in the grain boundary during the milling process.

The influence of the temperature and the heat treatment time on the Al64Cu23Fe13quasicrystal stability is studied in the present work. For this purpose the samples obtained by arc-furnace undergo different heat treatments varying the time and temperature of treatment. The structural characterization of the samples were carried out employing X-ray diffraction, and scanning electron microscopy, whereas the elemental composition was determined using energy dispersive x-ray spectroscopy. The results indicate that heat treatments are necessary to eliminate spurious phases which are always present after the synthesis of the samples. We also found that heat treatments of 800 ◦C by 48 hours or 700 ◦C by 168 hours are the most convenient ways to obtain samples with larger grain sizes (90 nm). Finally, the elemental analysis indicates a light deviation of the ideal composition due to the synth...

In the present work we study the influence of the unfolding procedure on the electronic level spacing statistics of silver nanoparticles (in their most stable configuration) with 923 and 2057 atoms, which were obtained employing molecular dynamics simulation with a tighet-binding potential. The results indicate that there is a strong dependence of the Brody parameter with the degree "n" of the polynomial used to make the unfolding procedure, especially for small n. For n=>6 the Brody parameter, independently of the nanoparticle sizes, remains almost constant. Thus, it was determined that the Brody parameter is close to the value corresponding to the Wiguer distribution, which is expected for systems in the metallic regime.

C.V.L. y H.N. agradecen a FONDECYT (CONCYTEC) por el soporte financiero a trav?s del Programa ?Centros de Excelencia?.

In this work we study theoretically the ferromagnetic resonance in a spin-valve. For this purpose, we propose a phenomenological model for the density of Helmholtz free energy taking into account the magnetocrystalline anisotropy, shape anisotropy, interlayer exchange coupling and exchange bias. Considering this energy density we solve the Landau-Lifshitz equation in spherical coordinates and in the resonance condition. In this way, we obtain the dispersion relation and, as a consequence, the frequency versus the resonance field. These results are in good agreement with the literature. Additionally, we apply the model to the IrMn/Co/Ru/NiFe system and study the magnetic coupling interlayers, where the non-magnetic layer (Ru) has a thickness of 3.2 nm. The results indicate the existence of an antiferromagnetic coupling with a strength of couping of Jbl + 2Jbc = −4.3 erg/cm2.

Alloys Fe-Al in the compositions Al25Fe75, Al50Fe50 and Al75Fe25 were synthesized by the arc furnace technique and the thermally treating 6000C. X-ray diractogram (XRD) and Mössbauer spectroscopy (MS) show the formation of the solid solution Fe(Al) rich and poor in aluminion. Tn the process of mechanical grinding to 10 hours milling maghemite γ − Fe2O3(Al) for compositions Al25Fe75 and Al50Fe50 with aluminiun atoms occupy some iron sites. In the case of the composition Al75Fe25 a single intermetallic Al13Fe4 is observed, remaining structurally invariant for all time nanostructuring.

An alternative method to determine the critical cooling rate of materials has been developed by explaining the size and cooling rate dependences of physical properties of metallic nanoparticles through the scaling theory. This method has been applied to silver and copper nanoparticles which have been obtained by molecular dynamics simulations. The results reveal that our values for critical rate are close for each studied physical quantity. Thus, by taking the average among them, we obtain 6.2(8) × 1012 K/s for silver and 8.9(5) × 1012 K/s for copper. We have also found the threshold size of nanoparticle behavior is independent of the cooling rate.

In this paper we study the influence of cooling rate on the structural properties of silver nanowires with 1.6 nm of diameter. This study is done employing molecular dynamics methods with a tight-binding potential. The cooling rates used are in the range of 0.25-25 K/ps. The structural analysis of these systems is performed studying the pair correlation function and the pair analysis technique. The results indicate that the cooling rate affects significantly the structural properties of silver nanowires finding two representative rates, the rupture rate of 2.55 K/ps, where the nanowire is broken into two nanoparticles, and the collapse rate of 1.73 K/ps, where the two nanoparticles collapse to one spherical nanoparticle.

This paper presents a comparative study of two pre-Columbian pottery styles which were associated at the Maranga Complex: Lima and Chakipampa, that initially was believed to be produced in Ayacucho. However, using physical techniques (diffraction and fluorescence X-ray) could be determined that they were produced with local raw materials specific to the Rimac valley, showing significant differences with the results of Chakipampa style pottery fragments recovered from the site Conchopata, Ayacucho.

This work has been partially supported by the Brazilian agencies CNPq and CAPES. H.S.T. thanks to the Peruvian Doctoral Scholarship of CIENCIACTIVA (CONCYTEC) under Grant #218-2014-FONDECYT. C.V.L. and J.Q-M are grateful to CIENCIACTIVA (CONCYTEC) for financial support throught the Excellence Center Programs. We also acknowledge E.B. Saitovitch and CBPF for experimental facilities.

In the present work we determine the threshold of the nanoparticle behavior of copper nanoparticles by studying their structural and electronic properties. The studied nanoparticles contain from 13 to 8217 atoms and were obtained by molecular dynamics simulations using the Johnson potential for copper based on the embedded atom method. The results indicate that for small copper nanoparticles (o1000 atoms, 2.8 nm) the surface plays an important role in their physical properties. Whereas, for large nanoparticles (42000 atoms, 3.5 nm), with spherical-like external shape and large percentage of fcc-like local structure, this effect is negligible and their electronic character are similar to such expected in solid copper. Finally, it has also been shown that copper nanoparticles change their electronic character, from metallic to insulating, after increasing the strength of the chemical disor...

In this work, we study the synthesis process and structural and magnetic characterization of the ?-Al5Fe2 intermetallic alloy obtained by the arc-melting technique. Subsequently, in order to obtain homogeneous crystalline phase, all melted samples were annealed at 847?C during 2 days, and then quenched into water. The structural and micro-structural characterization of the samples were performed by X-ray diffraction and,57Fe transmission Mössbauer spectroscopy, while the morphological study was performed using scanning electron microscopy. Moreover, magnetic characterization was carried out using vibrating sample magnetometer. X-ray fluorescence was employed for elemental characterization. The results indicate that it is possible to employ the arc-melting technique to synthesize the ?-Al5Fe2 intermetallic phase with high structural quality: orthorhombic crystalline structure and Cmcm sp...

L.M.S. thanks to the International Max Planck Research School Dynamical processes in atoms, molecules and solids and the Deutscher Akademischer Austauschdienst(DAAD) for the financial support. G.C.S. and C.V.L. are grateful to National Council of Science and Technology (CONCYTEC) from Peru for the financial support through the Doctoral Program for Peruvian Universities (Nº 218-2014-CONCYTEC) and the Peruvian Excellence Center Program, respectively. This work has also been partly supported by the German Research Foundation(DFG) within the Cluster of Excellence “Center for Advancing Electronics Dresden”. We acknowledge the Center for Information Services and High Performance Computing (ZIH) at TU Dresden for computational resources.

D. R. would like to thank the Condensed Matter Research Group of San Marcos University, where part of this work was performed. G. C. -S., H. S. T., and R. M. E. -B. are grateful to National Council of Science and Technology (CONCYTEC) from Peru for the financial support through the Doctoral Program for Peruvian Universities (Nro 218–2014-CONCYTEC). C. V. L. and D. R. are grateful to the Programa Nacional de Innovación para la Competitividad y Productividad of the Peruvian Agency Innovate Perú for financial support under contract number Nro. 457-PNICP-ECIP-2015. C. V. L. would also like to thanks the San Marcos University for partial financial support under project number B17130021.

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.

L. M. S. gratefully acknowledges the International Max Planck Research School Dynamical processes in atoms, molecules and solids and the Deutscher Akademischer Austauschdienst (DAAD) for the financial support. G. C. S. and C. V. L. are grateful to the National Council of Science and Technology (CONCYTEC) from Peru for the financial support through the Doctoral Program for Peruvian Universities (No. 218-2014-FONDECYT) and the Peruvian Excellence Center Program, respectively. This work has also been partly supported by the German Research Foundation (DFG) within the Cluster of Excellence “Center for Advancing Electronics Dresden”. We acknowledge the Center for Information Services and High Performance Computing (ZIH) at TU Dresden for computational resources. Open Access funding provided by the Max Planck Society.

The Judd-Ofelt analysis is essential becauseit indicates the influence of rare earth iondoping on the host matrix in which they arefound. In the present work, the results of theoptical characterization of zinc-tellurite glassesdoped with Yb3+ are presented, varying theconcentrations of Tm3+ and Er3+ by means of UVVISabsorption spectroscopy and refractive indexmeasurements. From these results, the Judd-Ofeltparameters were obtained, which indicated astructural modification with the addition of rareearth ions in the tellurite glassy matrix, due tothe rearrangement of the glassy structure and thebreaking of Te-O bonds.

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...