Person: Favieres Ruiz, Cristina
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Favieres Ruiz
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Cristina
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Ciencias
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InaMat2. Instituto de InvestigaciĆ³n en Materiales Avanzados y MatemĆ”ticas
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0000-0002-4500-0798
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2336
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Publication Open Access Vanadium trapped by oblique nano-sheets to preserve the anisotropy in Co-V thin films at high temperature(Elsevier, 2022) Favieres Ruiz, Cristina; Vergara Platero, JosĆ©; MagĆ©n, CĆ©sar; Ibarra, Manuel Ricardo; Madurga PĆ©rez, Vicente; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad PĆŗblica de Navarra / Nafarroako Unibertsitate PublikoaIn this study, oriented nano-sheets generated during the growth of cobalt-rich CoāV and CoāZn thin films induced a large anisotropy in the magnetic and transport properties. The regular nano-sheets were tilted 52ā54 deg. with respect to the substrate plane, ā 3.0ā4.0 nm thick, ā 30ā100 nm wide, and ā 200ā300 nm long, with an inter-sheet distance of ā 0.9ā1.2 nm. In spite of the different microstructures of the two kinds of samples where the CoāV films were amorphous, whereas the CoāZn films showed a growth of Zn nanocrystals, the oblique nano-sheet morphology conferred noticeable shape anisotropy to both specimens. This anisotropy resulted in an in-plane uniaxial magnetic anisotropy. The changes in the nano-morphology caused by thermal treatments, and hence in their anisotropic properties, were studied. While the CoāV samples retained or increased their magnetic and transport anisotropies, this anisotropic behavior vanished for the annealed CoāZn films. High resolution transmission electron microscopy, HRTEM, including chemical analysis at the nano-scale, and the dependence of the anisotropic resistance on temperature allowed to establish the nature and the activation energy spectra of the atomic relaxation processes during heating. These processes displayed a single peak at 1.63 eV for the CoāV and two peaks at 1.67 and 2.0 eV for the CoāZn. These spectra and their singularities were associated to the changes induced in the nano-morphology of the films by thermal treatments. The CoāV films retained their nano-sheet morphology almost up to 500 ĀŗC; the CoāZn films lost their nano-sheets at 290 ĀŗC. The thermal stability exhibited by the CoāV films makes them useful for applications in ultra high frequency, optical, magnetostrictive and magnetoelectric devices.Publication Open Access Generation of highly anisotropic physical properties in ferromagnetic thin films controlled by their differently oriented nano-sheets(American Institute of Physics, 2024) Favieres Ruiz, Cristina; Vergara Platero, JosĆ©; MagĆ©n, CĆ©sar; Ibarra, Manuel Ricardo; Madurga PĆ©rez, Vicente; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2We fabricated ferromagnetic nano-crystalline thin films of Co, Fe, CoāFe and Co-rich and Fe-rich, CoāMT and FeāMT (MT = transition metal), constituted by nano-sheets with a controlled slant. Visualization of these nano-sheets by Scanning Tunneling Microscopy and HighResolution Transmission Electron Microscopy (HRTEM) showed typically tilt angles ā56ā with respect to the substrate plane, and nano-sheets ā3.0ā4.0 nm thick, ā30ā100 nm wide, and ā200ā300 nm long, with an inter-sheet distance of ā0.9ā1.2 nm, depending on their constitutive elements. Induced by this nano-morphology, these films exhibited large uniaxial magnetic anisotropy in the plane, the easy direction of magnetization being parallel to the longitudinal direction of the nano-sheets. In the as-grown films, typical values of the anisotropy field were between Hk ā 48 and 110 kA/m depending on composition. The changes in the nano-morphology caused by thermal treatments, and hence in the anisotropic properties, were also visualized by HRTEM, including chemical analysis at the nano-scale. Some films retained their nano-sheet morphology and increased their anisotropies by up to three times after being heated to at least 500 āC: for example, the thermal treatments produced crystallization processes and the growth of CoV and CoFe magnetic phases, maintaining the nano-sheet morphology. In contrast, other annealed films, Co, Fe, CoZn, CoCu. . . lost their nano-sheet morphology and hence their anisotropies. This work opens a path of study for these new magnetically anisotropic materials, particularly with respect to the nano-morphological and structural changes related to the increase in magnetic anisotropy.Publication Open Access Structurally oriented nano-sheets in Co thin films: changing their anisotropic physical properties by thermally-induced relaxation(MDPI, 2017) Vergara Platero, JosĆ©; Favieres Ruiz, Cristina; MagĆ©n, CĆ©sar; Teresa, JosĆ© MarĆa de; Ibarra, Manuel Ricardo; Madurga PĆ©rez, Vicente; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; FĆsicaWe show how nanocrystalline Co films formed by separated oblique nano-sheets display anisotropy in their resistivity, magnetization process, surface nano-morphology and optical transmission. After performing a heat treatment at 270 Ā°C, these anisotropies decrease. This loss has been monitored measuring the resistivity as a function of temperature. The resistivity measured parallel to the direction of the nano-sheets has been constant up to 270 Ā°C, but it decreases when measured perpendicular to the nano-sheets. This suggests the existence of a structural relaxation, which produces the change of the Co nano-sheets during annealing. The changes in the nano-morphology and the local chemical composition of the films at the nanoscale after heating above 270 Ā°C have been analysed by scanning transmission electron microscopy (STEM). Thus, an approach and coalescence of the nano-sheets have been directly visualized. The spectrum of activation energies of this structural relaxation has indicated that the coalescence of the nano-sheets has taken place between 1.2 and 1.7 eV. In addition, an increase in the size of the nano-crystals has occurred in the samples annealed at 400 Ā°C. This study may be relevant for the application in devices working, for example, in the GHz range and to achieve the retention of the anisotropy of these films at higher temperatures.