Fabrication and characterization of magnetic thin films and multilayers

135 p.Los objetivos principales de esta tesis han sido por un lado la fabricación de películas y multicapas magnéticas de alta calidad y con alta reproducibilidad a la nanoescala y, por otro lado, la comprensión y modelización de los fenómenos magnéticos a dicha escala. En la primera parte se han estudiado las propiedades magnéticas de películas epitaxiales de aleaciones de cobalto y cromo, y sus dependencias con la composición y temperatura. Dichas muestras presentan una composición que posee un perfil de profundidad similar al de una ¿bañera¿. El estudio muestra que las propiedades magnéticas varían en función de la profundidad, siguiendo el perfil de la composición de cromo. En la segunda parte, se ha estudiado el proceso de inversión de la magnetización en función de la temperatura y del ángulo de aplicación del campo magnético externo en muestras de cobalto y cobalto-rutenio. Detalladas simulaciones micromagnéticas han complementado los resultados experimentales y han permitido la identificación de tres fases magnéticas diferentes cuyo punto de coexistencia es tricrítico en su naturaleza. En la última parte, se ha demostrado la inversión de la magnetización de superficie por medio del campo magnético en capas finas de Cr2O3, descubriendo una dependencia gigante con la temperatura del campo coercitivo. Este efecto resultaría óptimo para la técnica de grabación magnética asistida por calor. Además, hemos investigado películas epitaxiales de Cr2-xAlxO3, observando que la temperatura crítica se puede modificar mediante la aleación de Al2O3 utilizando la magnetización de superficie como una sonda para estudiar la transición de fase antiferromagnética.CICnanoGun

Giant temperature dependence of the spin reversal field in magnetoelectric chromia

Magnetic field-induced reversal of surface spin polarization for the magnetoelectric antiferromagnet chromia is studied via magnetometry in (0001)-textured thin films of various thicknesses. Reversal solely by magnetic means has been experimentally evidenced in sufficiently thin films. It sets the field-response of chromia films apart from bulk behavior, where switching between time-reversed single domain states requires the simultaneous presence of electric and magnetic fields. In our detailed experiments, we furthermore observe a giant sensitivity of the coercive field on temperature, thus, indicating the potential of magnetoelectric antiferromagnets as promising candidates for energy assisted magnetic recording media

Magnetic field induced switching of the antiferromagnetic order parameter in thin films of magnetoelectric chromia

A Landau-theoretical approach is utilized to model the magnetic field induced reversal of the antiferromagnetic order parameter in thin films of magnetoelectric antiferromagnets. A key ingredient of this peculiar switching phenomenon is the presence of a robust spin polarized state at the surface of the antiferromagnetic films. Surface or boundary magnetization is symmetry allowed in magnetoelectric antiferromagnets and experimentally established for chromia thin films. It couples rigidly to the antiferromagnetic order parameter and its Zeeman energy creates a pathway to switch the antiferromagnet via magnetic field application. In the framework of a minimalist Landau free energy expansion, the temperature dependence of the switching field and the field dependence of the transition width are derived. Least-squares fits to magnetometry data of (0001) textured chromia thin films strongly support this model of the magnetic reversal mechanism

Fabrication and characterization of magnetic thin films and multilayers

135 p.Los objetivos principales de esta tesis han sido por un lado la fabricación de películas y multicapas magnéticas de alta calidad y con alta reproducibilidad a la nanoescala y, por otro lado, la comprensión y modelización de los fenómenos magnéticos a dicha escala. En la primera parte se han estudiado las propiedades magnéticas de películas epitaxiales de aleaciones de cobalto y cromo, y sus dependencias con la composición y temperatura. Dichas muestras presentan una composición que posee un perfil de profundidad similar al de una ¿bañera¿. El estudio muestra que las propiedades magnéticas varían en función de la profundidad, siguiendo el perfil de la composición de cromo. En la segunda parte, se ha estudiado el proceso de inversión de la magnetización en función de la temperatura y del ángulo de aplicación del campo magnético externo en muestras de cobalto y cobalto-rutenio. Detalladas simulaciones micromagnéticas han complementado los resultados experimentales y han permitido la identificación de tres fases magnéticas diferentes cuyo punto de coexistencia es tricrítico en su naturaleza. En la última parte, se ha demostrado la inversión de la magnetización de superficie por medio del campo magnético en capas finas de Cr2O3, descubriendo una dependencia gigante con la temperatura del campo coercitivo. Este efecto resultaría óptimo para la técnica de grabación magnética asistida por calor. Además, hemos investigado películas epitaxiales de Cr2-xAlxO3, observando que la temperatura crítica se puede modificar mediante la aleación de Al2O3 utilizando la magnetización de superficie como una sonda para estudiar la transición de fase antiferromagnética.CICnanoGun

Boundary magnetization properties of epitaxial Cr2−xAlxO3 thin films

The magnetoelectric antiferromagnet α-Cr2O3 (chromia) is known to possess a roughness insensitive net equilibrium magnetization at the (0001) surface, called boundary magnetization (BM), which is coupled to the bulk antiferromagnetic order parameter. In order to verify whether this symmetry sensitive BM persists in alloys, we investigate the impact of diamagnetic dilution on chromia thin films alloyed with the isostructural α-Al2O3 (alumina). Single-crystalline Cr2−xAlxO3 thin films with (0001) surface orientation and varying stoichiometry have been grown by sputter codeposition in the concentration range between x = 0 and x = 0.6. For these samples, we find the corundum crystal structure, the antiferromagnetic ordering, and the boundary magnetization to be preserved. We also find that the critical temperature TN can be tuned by alloying with α-Al2O3, using the BM as a probe to study the magnetic phase transition. Furthermore, we were able to evaluate the critical exponent and the absolute BM values for different samples. Both properties corroborate that the observed magnetic signals originate from the BM rather than the bulk of the samples

Giant temperature dependence of the spin reversal field in magnetoelectric chromia

Magnetic field-induced reversal of surface spin polarization for the magnetoelectric antiferromagnet chromia is studied via magnetometry in (0001)-textured thin films of various thicknesses. Reversal solely by magnetic means has been experimentally evidenced in sufficiently thin films. It sets the field-response of chromia films apart from bulk behavior, where switching between time-reversed single domain states requires the simultaneous presence of electric and magnetic fields. In our detailed experiments, we furthermore observe a giant sensitivity of the coercive field on temperature, thus, indicating the potential of magnetoelectric antiferromagnets as promising candidates for energy assisted magnetic recording media

Current Status and Future Perspective on Lithium Metal Anode Production Methods

Lithium metal batteries (LMBs) are one of the most promising energy storage technologies that would overcome the limitations of current Li-ion batteries, based on their low density (0.534 g cm−3), low reduction potential (−3.04 V vs Standard Hydrogen Electrode) as well as their high theoretical capacities (3860 mAh g−1 and 2061 mAh cm−3). The overall cell mass and volume would be reduced while both gravimetric and volumetric energy densities would be greatly improved. Their electrochemical performance, however, is hampered by the low efficiency at high current densities and continuous degradation, which are related, among other factors, to the properties of the lithium metal anode (LMA). Hence, the production and processing of LMAs is crucial to obtain the desired properties that would enable LMBs. Here, the conventional method used for the production of LMAs, which is the combination of extraction, electrowinning, extrusion, and rolling processes, is reviewed. Then, the advances in the different alternative methods that can be used to produce and improve the properties of LMAs are described, which are divided into vapor phase, liquid phase, and electrodeposition. Within this last method, the anode-less concept, for which different approaches to the development of advanced current collectors are illustrated, is included.I.R.L. acknowledges the support of the Ministerio de Ciencia, Innovación y Universidades (No. PID2019-107468RB-C21) and Gobierno Vasco/Eusko Jaurlaritza (No. IT1546-22). This project has received funding from the Basque Government within the ELKARTEK 2021 call (project CICe2021) under the application number KK-2021/00064

Asymptomatic and symptomatic deep venous thrombosis in hospitalized acutely ill medical patients: risk factors and therapeutic implications

Background Acutely ill medical patients experience deep venous thrombosis (DVT) during the hospitalization, however the time course of DVT is still unclear. Objectives To evaluate risk factors in acutely ill hospitalized medical patients for proximal asymptomatic DVT (ADVT) and symptomatic DVT (SDVT) at admission and discharge. Patients/Methods In this prospective observational study, consecutive acutely ill medical patients (hospitalized mainly for acute medical disease as infections, neoplasm, anemia, heart failure) underwent compression ultrasonography (CUS) of proximal lower limb veins within 48 h from admission and at discharge to diagnose ADVT and SDVT. Covid-19 patients, anticoagulant therapy, surgical procedures, acute SDVT, and acute pulmonary embolism, were exclusion criteria. Biographical characteristics at hospitalization, D-Dimer (assessed by ELISA)) and DD-improve score. Results Of 2,100 patients (1002 females, 998 males, age 71 +/- 16 years) 58 (2.7%) had proximal ADVT at admission. Logistic regression analysis showed that age, and active cancer were independently associated with ADVT at admission. The median length of hospitalization was 10 days [interquartile range: 6-15]. During the hospital stay, 6 patients (0.3%) with a negative CUS at admission experienced DVT (2 SDVT and 4 ADVT). In the subgroup of patients (n = 1118), in whom D-dimer was measured at admission, D-Dimer and IMPROVE-DD score were associated with ADVT at admission (n = 37) and with all DVT (n = 42) at discharge. ROC curve defined an IMPROVE-DD score of 2.5 as the optimal cut-off for discriminating patients with and without thrombotic events. Conclusions We provide evidence of early development of ADVT in unselected acutely ill medical patients suggesting the need of investigating patients by CUS immediately after hospital admission (within 48 h). Advanced age, active cancer, known thrombophilia and increased IMPROVE-DD score may identify patients at risk. The benefit of anticoagulation needs to be investigated in patients with these specific risk factors and negative CUS at admission