Person:
Favieres Ruiz, Cristina

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https://academica-e.unavarra.es/handle/2454/49005

Last Name

Favieres Ruiz

First Name

Cristina

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Ciencias

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InaMat2. Instituto de Investigación en Materiales Avanzados y Matemáticas

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0000-0002-4500-0798

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2336

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Now showing 1 - 10 of 14

Open Access
Magnetic domain configurations of pulsed laser deposited MnBi hard magnetic films
(Elsevier, 2022) Madurga Pérez, Vicente; Favieres Ruiz, Cristina; Vergara Platero, José; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Hard magnetic MnBi films were obtained by appropriate heat treatments of pulsed laser deposited (PLD) (Bi/Mn) films. X-ray diffraction patterns indicated a slight texture of MnBi crystallites and magnetometry measurements showed a slight preferential growth of the crystallites with their c-axis perpendicular to the film plane. Magnetic force microscopy (MFM) measurements displayed the presence of magnetic domains, whose size was in the micrometer range, and which were correlated to the MnBi grains observed in the sample. The addition of extra Mn layers did not modify significantly the previous structural and magnetic results. Nevertheless, the size of the magnetic domains increased to a few microns. However, on adding extra Bi layers, upon annealing, the MnBi grains grew with their c-axes perpendicular to the film plane. A perpendicular to the film magnetic anisotropy was deduced from the hysteresis loops, where an increase in the remanence of the magnetization was measured when the magnetic field was applied perpendicular to the film plane. In these samples, by measuring the magnetic domain configuration of the samples by MFM, we observed that the size of the magnetic domains exceeded the dimensions of the grains. This change in the magnetic structure of the films was assumed to be due to the coupling of the magnetization in the neighboring grains, and it was responsible for the decrease of the coercivity in the Bi rich samples.
Open Access
Thermal hysteresis in the structural, magnetic and transport properties of hard magnetic MnBi films
(Elsevier, 2024-10-15) Vergara Platero, José; Favieres Ruiz, Cristina; Madurga Pérez, Vicente; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this work, the magnetic and transport properties associated with structural changes in MnBi hard magnetic films, with different Bi concentrations, were detailed. Two particular temperature regimes were studied. In the first place, at temperatures close to and below 260 °C (melting temperature of Bi in the samples) the resistance of the MnBi films underwent strong changes, showing thermal hysteresis, and depending on the amount of Bi in the samples. Thus, these resistance changes were attributed to the presence of unalloyed Bi in the samples. The maximum value of the relative change of resistance, ΔRI/R(T2) (where ΔRI=R(T1)-R(T2) being T1 and T2 the temperatures just immediately below and above the structural transition) was around 180 % for the sample with the highest Bi concentration. Second, at temperatures above 260 °C, both the magnetic moment and the resistance of the samples also showed significant changes around the transition from the Low Temperature (α-MnBi) to the High Temperature (β-MnBi) phase. These changes, which were attributed to this structural transition, also presented thermal hysteresis and also depended on the Bi concentration of the samples. However, contrary to the previous situation, the samples with the lowest amount of unalloyed Bi, and consequently with the highest value of the MnBi volume fraction presented a maximum value of the ΔRII/R(T4) ratio, (where ΔRII=R(T3)-R(T4) being T3 and T4 the temperatures immediately above and below the structural transition from the β to the α MnBi phase) this magnitude reaching a maximum value of 25 % for the sample with the lowest Bi content.
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
Influence of bi content on the temperature of the formation of the hard magnetic MnBi phase: simultaneous irreversible drop of resistance
(MDPI, 2022) Vergara Platero, José; Favieres Ruiz, Cristina; Madurga Pérez, Vicente; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Pulsed laser-deposited (PLD) MnBi films were fabricated by alternating deposition of Mn and Bi layers. In order to obtain the ferromagnetic MnBi phase, heat treatments were performed on the samples. Simultaneously, the resistance of the samples was monitored as a function of the temperature. Thus, on increasing the temperature, a steep decrease in the resistance of the films was observed, simultaneous to the onset of the formation of the MnBi phase. At room-temperature, these annealed samples showed a ferromagnetic behavior, as well as the presence of the characteristic LT-MnBi phase diffraction peaks in the X-ray diffraction patterns. The temperature of the generation of the MnBi phase depended on the relative concentration of Mn and Bi in the different samples: on increasing the Bi atomic concentration, the temperature of the generation of the MnBi phase decreased.
Open Access
Surface roughness influence on Néel-, crosstie, and Bloch-type charged zigzag magnetic domain walls in nanostructured Fe films
(MDPI, 2020) Favieres Ruiz, Cristina; Vergara Platero, José; Madurga Pérez, Vicente; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, PRO-UPNA18 (6105)
Charged magnetic domain walls have been visualized in soft magnetic nanostructured Fe thin films under both static and dynamic conditions. A transition in the core of these zigzagged magnetic walls from Néel-type to Bloch-type through the formation of crosstie walls has been observed. This transition in charged zigzagged walls was not previously shown experimentally in Fe thin films. For film thicknesses t < 30 nm, Néel-type cores are present, while at t ≈ 33 nm, walls with crosstie cores are observed. At t > 60 nm, Bloch-type cores are observed. Along with the visualization of these critical parameters, the dependence on the film thickness of the characteristic angle and length of the segments of the zigzagged walls has been observed and analyzed. After measuring the bistable magneto-optical behavior, the values of the wall nucleation magnetic field and the surface roughness of the films, an energetic fit to these nucleation values is presented.
Open Access
Three-dimensional finite element modelling of sheet metal forming for the manufacture of pipe components: symmetry considerations
(MDPI, 2022) Bhujangrao, Trunal; Veiga Suárez, Fernando; Penalva Oscoz, Mariluz; Costas, Adriana; Favieres Ruiz, Cristina; Ingeniería; Ingeniaritza
The manufacture of parts by metal forming is a widespread technique in sectors such as oil and gas and automotives. It is therefore important to make a research effort to know the correct set of parameters that allow the manufacture of correct parts. This paper presents a process analysis by means of the finite element model. The use case presented in this paper is that of a 3-m diameter pipe component with a thickness of 22 mm. In this type of application, poor selection of process conditions can result in parts that are out of tolerance, both in dimensions and shape. A 3D finite element model is made, and the symmetry of the tube section generated in 2D is analysed. As a novelty, an analysis of the process correction as a function of the symmetrical deformation of the material in this case in the form of a pipe is carried out. The results show a correct fitting of the model and give guidelines for manufacturing.
Open Access
High magnetic, transport, and optical uniaxial anisotropis generated by controlled directionally grown nano-sheets in Fe thin films
(American Institute of Physics, 2023) Favieres Ruiz, Cristina; Vergara Platero, José; Madurga Pérez, Vicente; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Fe films with thicknesses between 17 and 95 nm were grown with a nano-sheet morphology, which enabled their high uniaxial magnetic, transport, and optical in-plane anisotropies. The top edge of the nano-sheets was directly visualized as nano-string-like structures of approximately 12.5–14 nm width and 100–300 nm length. The hysteresis loops showed a clear easy direction of magnetization in the longitudinal direction of the nano-sheets, whereas the hard direction loops were anhysteretic, with no remanence and zero coercive field. The anisotropy field exhibited values between 70 and 111 kA/m depending on the thickness of the films, with the maximum value corresponding to a 34 nm thick sample. The resistance of the films was also found to be highly anisotropic. The ratio (R⊥–R||)/R|| was ≈86%, with R|| and R⊥ being the resistances in the parallel and perpendicular directions of the nano-sheets, respectively. Likewise, the reflectivity of the samples behaved anisotropically; the ratio (IReflmax–IReflmin)/IReflmax of the intensity of reflected light by the films reached up to 61% for 34 nm thick samples, achieving the maximum value, IReflmax, when the plane of the incident light coincided with the direction of the nano-sheets and the minimum, IReflmin, when this plane was perpendicular to the direction of the nano-sheets. The origin of these anisotropic behaviors was established. These anisotropic films with high magnetization and high uniaxial anisotropies at the nanoscale can be useful for microelectronics applications, for devices such as magnetic sensors and transducers, or for ultrahigh frequency inductors
Open Access
Application-oriented data analytics in large-scale metal sheet bending
(MDPI, 2023) Penalva Oscoz, Mariluz; Martín, Ander; Martínez, Víctor; Veiga Suárez, Fernando; Gil del Val, Alain; Ballesteros Egüés, Tomás; Favieres Ruiz, Cristina; Ingeniería; Ingeniaritza
The sheet-metal-forming process is crucial in manufacturing various products, including pipes, cans, and containers. Despite its significance, controlling this complex process is challenging and may lead to defects and inefficiencies. This study introduces a novel approach to monitor the sheet-metal-forming process, specifically focusing on the rolling of cans in the oil-and-gas sector. The methodology employed in this work involves the application of temporal-signal-processing and artificial-intelligence (AI) techniques for monitoring and optimizing the manufacturing process. Temporal-signal-processing techniques, such as Markov transition fields (MTFs), are utilized to transform time series data into images, enabling the identification of patterns and anomalies. synamic time warping (DTW) aligns time series data, accommodating variations in speed or timing across different rolling processes. K-medoids clustering identifies representative points, characterizing distinct phases of the rolling process. The results not only demonstrate the effectiveness of this framework in monitoring the rolling process but also lay the foundation for the practical application of these methodologies. This allows operators to work with a simpler characterization source, facilitating a more straightforward interpretation of the manufacturing process.
Open Access
Quest for amorphous superconductors of Bi-Sb alloys by irradiation with swift heavy ions
(AIP Publishing, 2025-03-17) Andrino-Gómez, Alberto; Tabares, Gema; Moratalla, Manuel ; Redondo-Cubero, Andrés; Madurga Pérez, Vicente; Favieres Ruiz, Cristina; Vergara Platero, José; García-López, Gastón; Gordillo, Nuria; Ramos, Miguel Ángel ; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Crystalline Bi100−xSbx alloys are known as the first discovered topological insulators, as well as for their promising thermoelectric properties, while their amorphous counterparts exhibit superconductivity (Tc > 6 K). However, their strong tendency to crystallize has hindered both the study and practical applications of amorphous Bi and Bi–Sb alloys. To explore the possibility of obtaining amorphous superconducting phases and enhancing thermoelectric properties, we investigated ion-beam irradiation as a method to induce amorphization in Bi100−xSbx alloys. We report irradiation experiments on pure Bi and Bi100−xSbx using bismuth and iodine ions (tens of MeV), generating an estimated vacancy damage of 40%–80%. Structural characterization and electrical resistivity measurements (2–300 K) revealed that, while amorphization and superconductivity were not achieved, melt-spun samples exhibited an order of magnitude higher conductivity than thermally evaporated ones. Moreover, ion-induced disorder further improved electrical conductivity, particularly in Bi90Sb10, highlighting its potential for thermoelectric applications.
Open Access
Tailoring magnetic and transport anisotropies in Co100−x –Cux thin films through obliquely grown nano-sheets
(MDPI, 2022) Favieres Ruiz, Cristina; Vergara Platero, José; Madurga Pérez, Vicente; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The magnetic and transport properties of pulsed laser-deposited Co100−x –Cux thin films were tailored through their nano-morphology and composition by controlling for the deposition geometry, namely normal or oblique deposition, and their Cu content. All films were composed of an amorphous Co matrix and a textured growth of Cu nanocrystals, whose presence and size d increased as x increased. For x = 50, all films were superparamagnetic, regardless of deposition geometry. The normally deposited films showed no in-plane magnetic anisotropy. On the contrary, controllable in-plane uniaxial magnetic anisotropy in both direction and magnitude was generated in the obliquely deposited films. The magnetic anisotropy field Hk remained constant for x = 0, 5 and 10, Hk ≈ 35 kAm−1, and decreased to 28 and 26 kAm−1 for x = 20 and 30, respectively. This anisotropy had a magnetostatic origin due to a tilted nano-sheet morphology. In the normally deposited films, the coercive field Hc increased when x increased, from 200 (x = 0) to 1100 Am−1 (x = 30). In contrast, in obliquely deposited films, Hc decreased from 1500 (x = 0) to 100 Am−1 (x = 30) as x increased. Activation energy spectra corresponding to structural relaxation phenomena in obliquely deposited films were obtained from transport property measurements. They revealed two peaks, which also depended on their nano-morphology and composition.