López García, Javier

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https://academica-e.unavarra.es/handle/2454/49434

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López García

First Name

Javier

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Física

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750421

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811110

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Now showing 1 - 9 of 9

Open Access
Influence of structural defects on the properties of metamagnetic shape memory alloys
(MDPI, 2020) Pérez de Landazábal Berganzo, José Ignacio; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Lambri, Osvaldo Agustín; López García, Javier; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
The production of µ-particles of Metamagnetic Shape Memory Alloys by crushing and subsequent ball milling process has been analyzed. The high energy involved in the milling process induces large internal stresses and high density of defects with a strong influence on the martensitic transformation; the interphase creation and its movement during the martensitic transformation produces frictional contributions to the entropy change (exothermic process) both during forward and reverse transformation. The frictional contribution increases with the milling time as a consequence of the interaction between defects and interphases. The influence of the frictional terms on the magnetocaloric effect has been evidenced. Besides, the presence of antiphase boundaries linked to superdislocations helps to understand the spin-glass behavior at low temperatures in martensite. Finally, the particles in the deformed state were introduced in a photosensitive polymer. The mechanical damping associated to the Martensitic Transformation (MT) of the particles is clearly distinguished in the produced composite, which could be interesting for the development of magnetically-tunable mechanical dampers.
Open Access
Room temperature huge magnetocaloric properties in low hysteresis ordered Cu-doped Ni-Mn-In-Co alloys
(Elsevier, 2022) La Roca, Paulo Matías; López García, Javier; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Rodríguez Velamazán, José Alberto; Pérez de Landazábal Berganzo, José Ignacio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Gobierno de Navarra / Nafarroako Gobernua, PC017–018 AMELEC
The reduction of the thermal hysteresis in first order magnetostructural transition is a determining factor to decrease energy losses and to improve the efficiency of magnetocaloric cooling based systems. In this work, a Cu doped NiMnInCo metamagnetic shape memory alloy (MMSMA) exhibiting a narrow thermal hysteresis (around 5 K) at room temperature has been designed. In this alloy, the induced L21 ordering process affects the phase stability in an unusual way compared to that observed in NiMnInCo and other NiMn based alloys. This ordering produces an increase in the Curie temperature of the austenite but hardly affects the mar tensitic transformation temperatures. As a consequence, the ordering increases the magnetization of the austenite without changing the transformation temperatures, doubles the sensitivity of the transformation to magnetic fields (the Claussius-Clapeyron slope goes from 2.1 to 3.9 K/T), improves the magnetocaloric effect, the reversibility and finally, enhances the refrigeration capacity. In addition, the magnetic hysteresis losses are among the lowest reported in the literature and the effective cooling capacity coefficient RCeff reaches 86 J/Kg for 2 T (15 % higher than those found in Ni-Mn based alloys) and 314 J/Kg for 6 T fields. Therefore, the ordered alloy possesses an excellent combination of low thermal hysteresis and high RCeff, not achieved previously in metamagnetic shape memory alloys near room temperature.
Open Access
Tailoring the structural and magnetic properties of Co-Zn nanosized ferrites for hyperthermia applications
(Elsevier, 2018) Gómez Polo, Cristina; Recarte Callado, Vicente; Cervera Gabalda, Laura María; Beato López, Juan Jesús; López García, Javier; Rodríguez Velamazán, José Alberto; Ugarte Martínez, María Dolores; Mendonça, E. C.; Duque, J. G. S.; Zientziak; Estatistika, Informatika eta Matematika; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Estadística, Informática y Matemáticas; Gobierno de Navarra / Nafarroako Gobernua
A comparative study of the magnetic properties (magnetic moment, magnetocrystalline anisotropy) and hyperthermia response in Co-Zn spinel nanoparticles is presented. The CoxZn1-xFe2O4 nanoparticles (x = 1, 0.5, 0.4, 0.3, 0.2 and 0.1) were synthesized by co-precipitated method and the morphology and mean crystallite size (around 10 nm) of the nanoparticles were analysed by TEM Microscopy. Regarding the magnetic characterization (SQUID magnetometry), Co-Zn nanoparticles display at room temperature anhysteretic magnetization curves, characteristic of the superparamagnetic behavior. A decrease in the blocking temperature, T-B, with Zn content is experimentally detected that can be ascribed to the reduction in the mean nanoparticle size as x decreases. Furthermore, the reduction in the magnetocrystalline anisotropy with Zn inclusion is confirmed through the analysis of TB versus the mean volume of the nanoparticles and the law of approach to saturation. Maximum magnetization is achieved for x = 0.5 as a result of the cation distribution between octahedral and tetrahedral spinel sites, analysed by neutron diffraction studies. The occurrence of a canted spin arrangement (Yafet-Kittel angle) is introduced to properly fit the magnetic spinel structures. Finally, the heating capacity of these spinel ferrites is analyzed under ac magnetic field (magnetic hyperthermia). Maximum SAR (Specific Absorption Rate) values are achieved for x = 0.5 that should be correlated to the maximum magnetic moment of this composition.
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
Boltzmann and the statistical multifractals
(UP4 Institute of Sciences, 2019) Río Correa, J. L. del; López García, Javier; Durán Meza, G.; Ciencias; Zientziak
We extend the Boltzmann’s ideas that describe the evolution to the equilibrium of many body systems to the multifractalde composition of the unitary intervalI, in terms of sets Jα conformed by points with the same pointwise dimension, and obtain the D (α) singularity spectrum.
Open Access
Routes for enhanced magnetism in Ni-Mn-In metamagnetic shape memory alloys
(Elsevier, 2019) López García, Javier; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Fabelo, O.; Cesari, Eduard; Rodríguez Velamazán, José Alberto; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
The authors provide in-depth physical insight into the enhancement of the magnetic properties of metamagnetic shape memory alloys produced by thermal treatment and cobalt doping. They use neutron scattering to study the atomic order and magnetic structures in the austenitic phases of Ni50Mn34In16 and Ni45Co5Mn37In13 alloys in two different states induced by thermal treatments. The increase of the magnetization in the austenite phase, particularly by cobalt doping, is explained by the enhanced ferromagnetic coupling between the magnetic moments located in octahedral sites. The spin density maps obtained from polarized neutron diffraction reveal the magnetic interaction pathways responsible for this coupling scheme.
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
Influence of microstructure in the martensitic transformation and in the physical and magnetic properties in metamagnetic shape memory alloys
(2019) López García, Javier; Recarte Callado, Vicente; Rodríguez Velamazán, José Alberto; Ciencias; Zientziak
In this work we have focused in the study of the influence of the microstructure in metamagnetic shape memory alloys (Ni-Mn-In and Ni-Mn-Sn systems) together with the effect of Co-doping, in order to gain insight into these effects and to control and improve the properties of these materials. Starting with the ternary Ni-Mn-Sn system, we have stablished the correlation between microstructural parameters and magnetostructural properties in these alloys. We have characterized the different microstructural states induced by thermo-mechanical treatments and correlated them with the properties of the alloys. The cobalt-doped quaternary system, Ni-Co-Mn-Sn-Co has been the next subject of study. With the aim of obtaining further understanding of the effect of Cobalt doping the magnetic coupling, we have selected the Ni-Mn-In system as case study. Since in the systematic study of the effect of milling we have observed that long milling times lead to amorphous states, we have extended our study to the recrystallization processes in Ni-Co-Mn-Sn and Ni-Co-Mn-In alloys, with the analysis of the evolution of the different phases, the cell parameters and microstrutural parameters as grain size, micro and macrostrains.
Open Access
The self-similarity properties and multifractal analysis of DNA sequences
(UP4 Institute of Sciences, 2019) Río Correa, J. L. del; López García, Javier; Durán Meza, G.; Ciencias; Zientziak
In this work is presented a pedagogical point of view of multifractal analysis deoxyribonucleic acid (DNA) sequences is presented. The DNA sequences are formed by 4 nucleotides (adenine, cytosine, guanine, and tymine). Following Jeffrey’s paper we associated a simple contractive function to each nucleotide, and constructed the Hutchinson’s operator W, which was used to build covers of different sizes of the unitary square Q, thus Wk (Q) is a cover of Q, conformed by 4k squares Qk of size 2−k, as each Qk corresponds to a unique subsequence of nucleotides with length k: b1b2...bk. Besides, it isobtained the optimal cover Ck to the fractal F generated for each DNA sequence was obtained. We made a multifractal decomposition of Ck in terms of the sets Jα conformed by the Qk’s with the same value of the Holder exponent α, and determined f(α), the Hausdorff dimension of Jα, using the curdling theorem.