Artículos de revista DF - FS Aldizkari artikuluak

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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
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
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
Changes in the crystalline degree in neutron irradiated EPDM viewed through infrared spectroscopy and inelastic neutron scattering
(Rede Latino-Americana de Materiais, 2018) Lambri, Osvaldo Agustín; Giordano, E. D.; Bonifacich, Federico Guillermo; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Física; Fisika; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The changes in the degree of crystallinity in commercial Ethylene Propylene Diene rubber-type M (EPDM) irradiated with neutrons at different doses has been studied by means of inelastic neutron scattering and infrared absorption spectroscopy experiments. EPDM samples were taken from the housing of non-ceramic electrical insulators which are used in outdoor transmission lines of 66 kV. Inelastic neutron scattering spectra were recorded at 5 K with an accessible energy-transfer range between 180 - 3500 cm-1. Infrared studies were performed at room temperature with an energy transfer between 4000 - 400 cm-1. Controlled neutron irradiation allows to obtain different volume fraction and size of crystalline zones in EPDM. The obtained results are discussed and correlated with studies of differential scanning calorimetry, dynamic mechanical analysis and positron annihilation lifetime spectroscopy from where the changes in crystallinity in EPDM were indirectly studied. Inelastic neutron scattering studies were not appropriate for determining the changes in the crystallinity degree in neutron irradiated commercial EPDM. In contrast, from infrared absorption spectroscopy the changes in crystallinity could be determined successfully.
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
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
Entropy change caused by martensitic transformations of ferromagnetic shape memory alloys
(MDPI, 2017) L'vov, Victor A.; Cesari, Eduard; Kosogor, Anna; Torrens Serra, Joan; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Física; Fisika
In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of martensitic transformation (MT), the characteristics of stress-induced MT, and the shear elastic modulus of SMA. The problem of separation of the magnetic contributions to the entropy change ΔS and heat Q exchanged in the course of martensitic transformation (MT) of SMA is considered in general terms, and theoretical formulas enabling the solution of the problem are presented. As an example, the ΔS and Q values, which were experimentally determined for Ni-Mn-Ga and Ni-Fe-Ga alloys with different Curie temperatures TC and MT temperatures TM, are theoretically analyzed. It is shown that for Ni-Mn-Ga martensites with TM < TC, the ratio of elastic and magnetic contributions to the entropy change may be greater or smaller than unity, depending on the temperature difference TC – TM.
Open Access
Evolution of magnetic response as a function of annealing temperature in Fe-based alloys
(Rede Latino-Americana de Materiais, 2018) Gargicevich, Damián; Bonifacich, Federico Guillermo; Lambri, Osvaldo Agustín; 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 magnetic response, coercive force and magnetic induction, in Fe-10at.% Si, Fe-6at.% Al-9at.% Si and Fe-4at.% Al-8at.% Ge alloys as a function of the annealing temperature was determined and correlated to the microstructural state. The microstructural characterization was made through differential thermal analysis, mechanical spectroscopy and neutron thermodiffraction studies. It has been determined that the increase in the order degree and the decrease in the mobility of structural defects lead to a deterioration of the magnetic quality of the alloys above detailed.
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
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
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
Giant direct and inverse magnetocaloric effect linked to the same forward martensitic transformation
(Springer Nature, 2017) Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Sánchez-Alarcos Gómez, Vicente; Beato López, Juan Jesús; Rodríguez Velamazán, José Alberto; Sánchez Marcos, J.; Gómez Polo, Cristina; Cesari, Eduard; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física
Metamagnetic shape memory alloys have aroused considerable attraction as potential magnetic refrigerants due to the large inverse magnetocaloric effect associated to the magnetic-field-induction of a reverse martensitic transformation (martensite to austenite). In some of these alloys, the austenite phase can be retained on cooling under high magnetic fields, being the retained phase metastable after field removing. Here, we report a giant direct magnetocaloric effect linked to the anomalous forward martensitic transformation (austenite to martensite) that the retained austenite undergoes on heating. Under moderate fields of 10 kOe, an estimated adiabatic temperature change of 9 K has been obtained, which is (in absolute value) almost twice that obtained in the conventional transformation under higher applied fields. The observation of a different sign on the temperature change associated to the same austenite to martensite transformation depending on whether it occurs on heating (retained) or on cooling is attributed to the predominance of the magnetic or the vibrational entropy terms, respectively.
Open Access
Influence of defects on the irreversible phase transition in the Fe-Pd doped with Co and Mn
(Rede Latino-Americana de Materiais, 2018) Bonifacich, Federico Guillermo; Lambri, Osvaldo Agustín; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Sánchez-Alarcos Gómez, Vicente; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The appearance of BCT martensite in Fe-Pd-based ferromagnetic shape memory alloys, which develops at lower temperatures than the thermoelastic martensitic transition, deteriorates the shape memory properties. In a previous work performed in Fe70Pd30, it was shown that a reduction in defects density reduces the non thermoelastic FCT-BCT transformation temperature. In the present work, the influence of quenched-in-defects upon the intensity and temperature of the thermoelastic martensitic (FCC-FCT) and the non thermoelastic (FCT-BCT) transitions in Fe-Pd doped with Co and Mn is studied. Differential scanning calorimetric and mechanical spectroscopy studies demonstrate that a reduction in the dislocation density the stability range of the FCC-FCT reversible transformation in Fe67Pd30Co3 and Fe66.8Pd30.7Mn2.5 ferromagnetic shape memory alloys.
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
Loss of ductility due to the decarburation and Mn depletion of a coarse-grained TWIP steel
(Consejo Superior de Investigaciones Científicas (CSIC), 2017) Cuevas Jiménez, Fernando de las; Gil Sevillano, Javier; Física; Fisika
Se ha observado una clara transición de la ductilidad a tracción con el tamaño de grano D del orden 15 μm - 20 μm (1,50 μm ≤ D < 50 μm) en un acero TWIP, 22% de Mn, 0,6% de C (% en masa). Este comportamiento es una combinación de un efecto intrínseco del tamaño de grano D en la resistencia y el endurecimiento por deformación del material, con un efecto extrínseco, proceso de descarburación superficial y pérdida de Mn ocurrido durante los tratamientos de recocido a T ≥ 1000 ºC. En el presente trabajo se ha estudiado en profundidad este efecto extrínseco sucedido en el acero TWIP. Se han realizado análisis por GDOES (Espectroscopia Óptica de Descarga Luminiscente) para estudiar cuantitativamente los perfiles de concentración de C y Mn. La profundidad de descarburación superficial se ha modelizado usando la teoría de Birks-Jackson. Se ha observado vía ferritoscopio que, en el volumen descarburizado, coexisten dos microconstituyentes: α’-martensita y γ-austenita. La ductilidad del acero TWIP de tamaño de grano grosero, sometido a altas temperaturas y largos tiempos de recocido, disminuye como consecuencia de la formación de α’-martensita y γ-austenita menos estable con menor energía de defectos de apilamiento, EDA, debido a la pérdida de Mn en el volumen descarburizado.
Open Access
Low field magnetic and thermal hysteresis in antiferromagnetic dysprosium
(MDPI, 2017) Liubimova, Iuliia; Corró Moyá, Miguel; Torrens Serra, Joan; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Kustov, Sergey; Física; Fisika
Magnetic and thermal hysteresis (difference in magnetic properties on cooling and heating) have been studied in polycrystalline Dy (dysprosium) between 80 and 250 K using measurements of the reversible Villari effect and alternating current (AC) susceptibility. We argue that measurement of the reversible Villari effect in the antiferromagnetic phase is a more sensitive method to detect magnetic hysteresis than the registration of conventional B(H) loops. We found that the Villari point, recently reported in the antiferromagnetic phase of Dy at 166 K, controls the essential features of magnetic hysteresis and AC susceptibility on heating from the ferromagnetic state: (i) thermal hysteresis in AC susceptibility and in the reversible Villari effect disappears abruptly at the temperature of the Villari point; (ii) the imaginary part of AC susceptibility is strongly frequency dependent, but only up to the temperature of the Villari point; (iii) the imaginary part of the susceptibility drops sharply also at the Villari point. We attribute these effects observed at the Villari point to the disappearance of the residual ferromagnetic phase. The strong influence of the Villari point on several magnetic properties allows this temperature to be ranked almost as important as the Curie and Néel temperatures in Dy and likely also for other rare earth elements and their alloys.
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
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
Magnetocaloric effect enhancement driven by intrinsic defects in a Ni45Co5Mn35Sn15 alloy
(Elsevier, 2019) Sánchez-Alarcos Gómez, Vicente; López García, Javier; Unzueta, Iraultza; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Beato López, Juan Jesús; García, José Ángel; Plazaola, Fernando; Rodríguez Velamazán, José Alberto; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física
The influence of mechanically-induced defects on the magnetostructural properties is analyzed in a Ni-Co-Mn-Sn alloy subjected to soft milling and subsequent annealing treatments. It is found that, opposite to what occurs in Ni-Mn-Sn ternary alloys, the annealing treatment affects the magnetic properties in a different way in martensite and in austenite. In particular, the saturation magnetization significantly increases in martensite after annealing whereas just a very slight variation is observed in austenite. This leads to the interesting fact that the presence of microstructural defects, far for worsening, makes the magnetocaloric effect to be higher in the as-milled state than after annealing. This behavior is explained as the result of the combination of the effect of defects on the Mn-Mn distance, the effect of Co on the magnetic exchange coupling between Mn atoms, and the effect of defects on the vibrational entropy change at the martensitic transformation.
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.