Dpto. Física - Fisika Saila

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Open Access
A field induced ferromagnetic-like transition below 2.8 K in Li2CuO2: an experimental and theoretical study
(AIP Publishing, 1998) Ortega Hertogs, Ricardo; Jensen, P. J.; Rao, K. V.; Sapiña, F.; Beltrán, D.; Iqbal, Z.; Cooley, J. C.; Smith, J. L.; Física; Fisika
The low temperature magnetic properties of the Li2CuO2 compound have been investigated by means of superconducting quantum interference device magnetometry. We find in addition to an antiferromagnetic phase below 9.5 K a ferromagnetic-like steep rise of the magnetization around 2.8 K. The observed low temperature behavior is discussed by considering second and fourth order magnetocrystalline effective anisotropy coefficients, in addition to the exchange couplings reported in the literature.
Open Access
Magnetic transition in nanocrystalline soft magnetic alloys analyzed via ac inductive techniques
(American Physical Society, 2004) Gómez Polo, Cristina; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Vázquez, M.; Hernando, A.; Física; Fisika; Gobierno de Navarra / Nafarroako Gobernua
The magnetic transition in a FeSiBCuNb nanocrystalline alloy, associated with the decoupling of ferromagnetic crystallites around the Curie point of the residual amorphous matrix, is analyzed in this work through the temperature dependence of the ac axial magnetic permeability and impedance of the samples. The temperature dependence of both complex magnitudes presents a maximum in the irreversible contribution at a certain transition temperature. While for low values of the exciting ac magnetic field the transition temperature lies below the Curie temperature of the amorphous phase, a shift above this Curie point is observed increasing the amplitude of the applied ac magnetic field. The detected field dependence is interpreted taking into account the ac nature of the inductive characterization techniques and the actual temperature dependence of the coercivity of the samples.
Open Access
Aspectos biopsicológicos de la infección por virus inmunodeficiencia humana (VIH)
(Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, 2006) Aparicio Ágreda, María Lourdes; Cuevas Jiménez, Carlos Pablo; Psicología y Pedagogía; Psikologia eta Pedagogia; Física; Fisika
El objetivo de este artículo es ofrecer una comprensión global de la infección por VIH. Si bien es un proceso inicialmente asintomático, el avance de la infección produce consecuencias a nivel de funcionamiento, en gran medida por las implicaciones psicológicas que conlleva. Por ello, se destaca la necesidad de una comprensión que abarque la evaluación e intervención psicológica de la persona con VIH y sus cuidadores como medio de mejorar la calidad de vida de todos ellos.
Open Access
Uncertainties caused by source directivity in room-acoustic investigations
(Acoustical Society of America (ASA), 2008) San Martín Murugarren, Ricardo; Arana Burgui, Miguel; Física; Fisika
Although deviations in the measurement of acoustic parameters should be lower than the subjectively perceivable change in the corresponding parameter measured, this study reflects that directionality of sound sources could cause wide audience areas to break away from this criterion at high frequencies, even when using dodecahedron loudspeakers which meet the requirements of the ISO 3382 standard. The directivity of four different acoustic sources was measured and the influence of its accurate orientation spatially quantified in five enclosures for speech and music. By means of simulation software, the number of receivers affected by uncertainties greater than difference limens was established.
Open Access
Are urban noise pollution levels decreasing?
(Acoustical Society of America, 2010) Arana Burgui, Miguel; Física; Fisika
The majority of acoustic impact studies developed over the last 50 years have used a similar acoustic parameter Leq, Ldn but the noise mapping methodology has been very uneven. The selection of the measurement points, the measurement periods, or the evaluation indices have not followed a unique criterion. Therefore, it is not possible to compare the sound pollution levels between different cities from those studies, at least in a rigorous sense. Even more, different studies carried out in the same city by different researchers during different years and using different methodologies are not conclusive whether the acoustic pollution increases or decreases. The present paper shows results, with statistical significance, about the evolution of the acoustic pollution obtained for two Spanish cities, Pamplona and Madrid. In both cases, it can be concluded that noise pollution decreases over time (P<0.01).
Open Access
Strategic noise map of a major road carried out with two environmental prediction software packages
(Springer Netherlands, 2010) Arana Burgui, Miguel; San Martín Murugarren, Ricardo; San Martín Erviti, María Luisa; Aramendía Santamaría, Emilio; Física; Fisika
The main objective of this study is to analyze the differences found in the results of noise mapping using two of the most popular software techniques for the prediction of environmental noise. The location selected to conduct the comparative study is an area encompassed by the ring road that surrounds the city of Pamplona and on a grid, with a total of 6 × 105 points, approximately. In fact, and as the Environmental Noise Directive points out, it is a major road designated by a Member State (Spain). Configuration of the calculation parameters (discretization of the sources, ground absorption, reflection order, etc.) was as equivalent as possible as far as programs allow. In spite of that, a great number of differences appear in the findings. Although in 95.5% of the points the difference in the noise level calculated from the two programs was less than 3 dB, this general statistic result concealed some great differences. These are due to the various algorithms that programs implement to evaluate noise levels. Most differences pertain to highly screened receivers or remote ones. In the former, the algorithm of visibility is the main cause of such differences. In the latter, differences are mainly brought about by a different implementation of the propagation under homogeneous and favorable atmospheric conditions from both software systems.
Open Access
Generating and measuring the anisotropic elastic behaviour of Co thin films with oriented surface nano-strings on micro-cantilevers
(Springer, 2011) Madurga Pérez, Vicente; Vergara Platero, José; Favieres Ruiz, Cristina; Física; Fisika
In this research, the elastic behaviour of two Co thin films simultaneously deposited in an off-normal angle method was studied. Towards this end, two Si micro-cantilevers were simultaneously coated using pulsed laser deposition at an oblique angle, creating a Co nano-string surface morphology with a predetermined orientation. The selected position of each micro-cantilever during the coating process created longitudinal or transverse nano-strings. The anisotropic elastic behaviour of these Co films was determined by measuring the changes that took place in the resonant frequency of each micro-cantilever after this process of creating differently oriented plasma coatings had been completed. This differential procedure allowed us to determine the difference between the Young's modulus of the different films based on the different direction of the nano-strings. This difference was determined to be, at least, the 20% of the Young's modulus of the bulk Co.
Open Access
Theoretical modeling and experimental verification of the scattering from a ferromagnetic microwire
(IEEE, 2011) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gómez Polo, Cristina; Labrador Otamendi, Alberto; Pérez de Landazábal Berganzo, José Ignacio; Gonzalo García, Ramón; Física; Fisika; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
This contribution presents a theoretical modelling of the scattering of ferromagnetic microwires in free-space and inside a rectangular waveguide, providing both an analytical solution and a physical interpretation of the problem. Special attention is devoted to the impact of the microwire radius and its magnetic properties. Theoretical results have been experimentally verified measuring the reflection, absorption and transmission coefficients of a ferromagnetic microwire inside a rectangular waveguide.
Open Access
A comprehensive analysis of the absorption spectrum of conducting ferromagnetic wires
(IEEE, 2012) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gómez Polo, Cristina; Labrador Otamendi, Alberto; Pérez de Landazábal Berganzo, José Ignacio; Gonzalo García, Ramón; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Física; Fisika
A detailed analysis of the absorption spectrum of conductive ferromagnetic wires is presented. The absorption spectrum is computed from the solution to the scattering problem, and circuit models are formulated to clarify the interplay between losses, skin-effect and wire geometry. Both infinitely-long wires and the axial resonances introduced by finite-length wires are considered. The theoretical results are validated experimentally through measurements within a metallic rectangular waveguide.
Open Access
Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers
(Springer, 2012) Vergara Platero, José; Favieres Ruiz, Cristina; Madurga Pérez, Vicente; Física; Fisika
In this study, the fabrication of magnetic multilayers with a controlled value of the in-plane uniaxial magnetic anisotropy field in the range of 12 to 72 kA/m was achieved. This fabrication was accomplished by the deposition of bilayers consisting of an obliquely deposited (54A degrees) 8-nm-thick anisotropic Co layer and a second isotropic Co layer that was deposited at a normal incidence over the first layer. By changing the thickness value of this second Co layer (X) by modifying the deposition time, the value of the anisotropy field of the sample could be controlled. For each sample, the thickness of each bilayer did not exceed the value of the exchange correlation length calculated for these Co bilayers. To increase the volume of the magnetic films without further modification of their magnetic properties, a Ta spacer layer was deposited between successive Co bilayers at 54A degrees to prevent direct exchange coupling between consecutive Co bilayers. This step was accomplished through the deposition of multilayered films consisting of several (Co8 nm-54A degrees/Co (X nm-0A degrees)/Ta6 nm-54A degrees) trilayers.
Open Access
Experimental Stark widths and shifts of Cr II spectral lines
(Oxford University Press, 2013) Aguilera Andoaga, José Antonio; Aragón Garbizu, Carlos; Manrique Rosel, Javier; Física; Fisika
Stark widths and shifts of Cr II lines with wavelengths in the range 2000–3500 Å have been determined by laser-induced breakdown spectroscopy. The spectra have been measured at different instants of the plasma evolution from 0.6 to 3.4 μs, at which the temperature and electron density are in the ranges 12 000–16 300 K and (0.89–8.2) × 10¹⁷ cm ˉ³, respectively. The laser-induced plasmas have been generated from three fused glass samples with different chromium concentrations, selected to control the self-absorption of the lines. The Stark widths and shifts are compared with the experimental and theoretical data available in the literature.
Open Access
Simple fabrication of ultrahigh aspect ratio nanostructures for enhanced antireflectivity
(American Vacuum Society, 2014) Domínguez Fernández, Sagrario; Cornago Santos, Ignacio; Bravo Larrea, Javier; Pérez Conde, Jesús; Choi, Hyungryul J.; Kim, Jeong-Gil; Barbastathis, George; Física; Fisika; Gobierno de Navarra / Nafarroako Gobernua: 1858/2012
In this work, the authors present a novel fabrication process to create periodic nanostructures with aspect ratio as high as 9.6. These nanostructures reduce spectral reflectance of silicon to less than 4% over the broad wavelength region from 200 to 2000nm. At the visible range of the spectrum, from 200 to 650 nm, reflectivity is reduced to less than 0.1%. The aspect ratio and reflectance performance that the authors achieved have never been reported before for ordered tapered nanostructures, to our knowledge.
Open Access
Síntesis, caracterización y aplicaciones de nanoestructuras magnéticas basadas en óxidos de metales de transición
(2014) Larumbe Abuin, Silvia; Gómez Polo, Cristina; Física; Fisika
Como objetivo principal de esta tesis se plantea la preparación de sistemas híbridos constituídos por nanoestructuras del tipo NM@SiO2@X-TiO2 (NM: núcleo magnético; X: elemento dopante) con actividad fotocatalítica en el visible y capaces de ser recuperados del medio de reacción mediante la acción de un campo magnético externo. Además, existen una serie de aspectos complementarios que han surgido en el desarrollo del trabajo que presentan un claro interés tanto desde una perspectiva básica como aplicada: Síntesis 1.1 Síntesis de nanopartículas magnéticas de composición Fe3O4/NiFe2O4 recubiertas con SiO2: análisis de las condiciones de síntesis empleando el método sol-gel que den lugar a las propiedades estructurales y magnéticas deseadas. 1.2 Síntesis de nanopartículas de TiO2 dopadas con Fe/N: preparación de nanopartículas de TiO2 mediante el método sol-gel con propiedades fotocatalíticas óptimas (absorción en el visible). 1.3 Síntesis de nanoestructuras híbridas Fe3O4@SiO2@TiO2: preparación de nanoestructuras híbridas mediante el recubrimiento con óxido de titanio de nanopartículas magnéticas previamente sintetizadas empleando dos métodos de calcinación: calcinación convencional y mediante hipertermia magnética. Caracterización básica 2.1 Análisis de los efectos superficiales en las propiedades magnéticas de las nanopartículas ferrimagnéticas: estudio del efecto del tamaño nanométrico de las nanopartículas magnéticas en las propiedades magnéticas (reducción de la imanación de saturación, fenómenos de spin-glass y exchange bias). 2.2 Análisis del efecto de los dopantes y de la relación de hidrólisis en la temperatura de transición anatasa-rutilo: evaluación del efecto de los elementos dopantes (Fe,N) en la temperatura de transición anatasa-rutilo con el objeto de reducir la fracción de rutilo con fines aplicados. 2.3 Análisis del efecto de los dopantes en el espectro de absorción de las nanopartículas de TiO2: estudio de la modificación introducida por los dopantes en el espectro de absorción de las nanopartículas de óxido de titanio con el objetivo de obtener absorción en la zona del visible. 2.4 Análisis del efecto de los dopantes en la observación de ferromagnetismo a 300 K en las nanopartículas de TiO2: estudio desde un punto de vista básico de la introducción de elementos metálicos (Fe) y elementos no metálicos (N) en las propiedades magnéticas de la fase anatasa. Observación de ferromagnetismo a temperatura ambiente. Aplicaciones 3.1 Obtención de nanoestructuras híbridas Fe3O4@SiO2@TiO2 con actividad fotocatalítica en el visible: análisis de la actividad fotocatalítica de las estructuras híbridas preparadas para su utilización bajo radiación visible. 3.2 Obtención de nanoestructuras híbridas susceptibles de ser recuperadas mediante la aplicaciones de un campo magnético externo: evaluar si las nanoestructuras híbridas con actividad fotocatalítica en el visible además son susceptibles de ser recuperadas con un campo magnético externo para poder ser reutilizadas.
Open Access
Long-range atomic order and entropy change at the martensitic transformation in a Ni-Mn-In-Co metamagnetic shape memory alloy
(MDPI, 2014) Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Cesari, Eduard; Rodríguez Velamazán, José Alberto; Física; Fisika
The influence of the atomic order on the martensitic transformation entropy change has been studied in a Ni-Mn-In-Co metamagnetic shape memory alloy through the evolution of the transformation temperatures under high-temperature quenching and post-quench annealing thermal treatments. It is confirmed that the entropy change evolves as a consequence of the variations on the degree of L21 atomic order brought by thermal treatments, though, contrary to what occurs in ternary Ni-Mn-In, post-quench aging appears to be the most effective way to modify the transformation entropy in Ni-Mn-In-Co. It is also shown that any entropy change value between around 40 and 5 J/kgK can be achieved in a controllable way for a single alloy under the appropriate aging treatment, thus bringing out the possibility of properly tune the magnetocaloric effect.
Open Access
CSigma graphs: a new approach for plasma characterization in laser-induced breakdown spectroscopy
(Elsevier, 2014) Aragón Garbizu, Carlos; Aguilera Andoaga, José Antonio; Física; Fisika
A generalization of curves of growth called CSigma (Cσ) graphs, which allows including several lines of various elements in the same ionization state at different concentrations, is proposed for laser-induced breakdown spectroscopy (LIBS) experiments. The method relies on the Boltzmann, Saha and radiative transfer equations for plasmas in local thermodynamic equilibrium. Cσ graphs are based on the calculation of a line cross section σl for each of the experimental data, starting from the atomic data of the line, the temperature and the electron density. A model of homogeneous plasma, applied separately for neutral atoms and ions, is used. A limit of validity is established for this model. Experimental Cσ graphs have been obtained using fused glass samples containing Fe, Mn, Mg, Si and Cr. By fitting experimental Cσ graphs to calculated curves, the LIBS system becomes characterized by a set of four parameters βA, Nl, T, Ne, different for neutral atoms and ions. Starting from this characterization, the intensity and self-absorption of a given spectral line of an element at a certain concentration may be predicted, provided that its atomic data are known and the limit of validity is not exceeded.
Open Access
People exposed to traffic noise in european agglomerations from noise maps: a critical review
(De Gruyter, 2014) Arana Burgui, Miguel; San Martín Murugarren, Ricardo; Salinas Hilburg, Juan Carlos; Física; Fisika
Two of the main objectives of the European Directive on environmental noise are, firstly, to unify acoustic indices for assessing environmental noise and, secondly, to standardize assessment methodologies. The ultimate goal is to objectively and comparably manage the impact and evolution of environmental noise caused both by urban agglomerations and by traffic infrastructures (roads, rails and airports). The use of common indices and methodologies (together with five-year plan assessment required by the authorities in charge) should show how noise pollution levels are evolving plus the effectiveness of corrective measures implemented in the action plans. In this paper, available results from numerous European agglomerations (with particular emphasis on Spanish agglomerations) are compared and analysed. The impact and its evolution are based on the percentage of people exposed to noise. More specifically, it demonstrates the impact caused by road traffic, which proves to be the main noise source in all agglomerations. In many cases, the results are extremely remarkable. In some case, the results are illogical. For such cases, it can be concluded that either assessment methodologies have been significantly amended or the input variables to the calculation programs have been remarkably changed. The uncertainty associated with the results is such that, in our opinion, no conclusions can be drawn concerning the effectiveness of remedial measures designed within the action plans after the Directive’s first implementation Phase.
Open Access
Method for measurement of transition probabilities by laser-induced breakdown spectroscopy based on CSigma graphs. Application to Ca II spectral lines
(Elsevier, 2015) Aguilera Andoaga, José Antonio; Aragón Garbizu, Carlos; Manrique Rosel, Javier; Física; Fisika
We propose a method for determination of transition probabilities by laser-induced breakdown spectroscopy that avoids the error due to self-absorption. The method relies on CSigma graphs, a generalization of curves of growth which allows including several lines of various elements in the same ionization state. CSigma graphs are constructed including reference lines of an emitting species with well-known transition probabilities, together with the lines of interest, both in the same ionization state. The samples are fused glass disks prepared from small concentrations of compounds. When the method is applied, the concentration of the element of interest in the sample must be controlled to avoid the failure of the homogeneous plasma model. To test the method, the transition probabilities of 9 Ca II lines arising from the 4d, 5s, 5d and 6s configurations are measured using Fe II reference lines. The data for 5 of the studied lines, mainly from the 5d and 6s configurations, had not been measured previously.
Open Access
Thermal degradation of type I collagen from bones
(Tech Science Press, 2016) Lambri, Melania Lucila; Giordano, E. D.; Bozzano, P. B.; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The denaturation processes of collagen in the temperature range between 450 K and 670 K are revealed through studies performed on cow rib bones by means of mechanical spectroscopy, differential scanning calorimetry, thermogravimetry, scanning electron microscopy and infrared spectroscopy. The conformational change of the collagen molecules from a triple helix structure to a random coil was found at around 510 K. It was determined that the transformation is developed through the viscous movement of fibrils with an activation energy of (127 ± 8) kJ/mol. The second stage of massive bulk deterioration of the collagen was found at around 600 K, which leads to the loss of the mechanical integrity of the bulk collagen. In addition, an easy-to-handle viscoelastic procedure for obtaining the activation energy of the denaturation process from mechanical spectroscopy studies was also shown.
Open Access
119Sn Mössbauer spectroscopy for assessing the local stress and defect state towards the tuning of Ni-Mn-Sn alloys
(AIP Publishing, 2017) Unzueta, Iraultza; López García, Javier; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física
The influence of defects and local stresses on the magnetic properties and martensitic transformation in Ni50Mn35Sn15 is studied at macroscopic and atomic scale levels. We show that both the structural and magnetic properties of the alloy are very sensitive to slight microstructural distortions. Even though no atomic disorder is induced by milling, the antiphase boundaries linked to dislocations promote the antiferromagnetic coupling of Mn, resulting in a significant decrease in the saturation magnetization. On the other hand, the temperature range of the transformation is considerably affected by the mechanically induced local stresses, which in turn does not affect the equilibrium temperature between the austenitic and martensitic phases. Finally, we demonstrate that the recovery of the martensitic transformation is directly related to the intensity of the non-magnetic component revealed by 119Sn Mössbauer spectroscopy. This result opens the possibility of quantifying the whole contribution of defects and the local stresses on the martensitic transformation in Ni-Mn-Sn alloys.
Open Access
Interferometric vs wavelength selective optical fiber sensors for cryogenic temperature measurements
(SPIE, 2017) Miguel Soto, Verónica de; Leandro González, Daniel; López Aldaba, Aitor; Beato López, Juan Jesús; Pérez de Landazábal Berganzo, José Ignacio; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; López-Amo Sáinz, Manuel; Ingeniaritza Elektrikoa eta Elektronikoa; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Ingeniería Eléctrica y Electrónica; Física
In this work, a preliminary study of the behavior of two different interferometric fiber optic sensors and two different wavelength selective fiber optic sensors is performed. A photonic cristal fiber Fabry-Pérot interferometer, a Sagnac interferometer, a commercial fiber Bragg grating (FBG) and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser are analyzed. A comparison of their sensitivities and resolutions is carried out to analyze their performance as sensors for cryogenic temperatures, taking into account their advantages and drawbacks.