Methods for the analysis of thermomagnetic phase transitions of magnetocaloric materials

This thesis focuses on the analysis of the relation between thermomagnetic phase transitions and magnetocaloric response of materials. First, various experimental factors that can a ect the measurements of the magnetocaloric e ect and can potentially cause misleading interpretation or artifacts are studied with the aid of experimental data and numerical calculations. These are sample geometry, compositional inhomogeneities, low temperature limitation in heat capacity measurements and measurement protocols in direct techniques. After that, it is shown that the analysis of the magnetic eld dependence of the magnetocaloric e ect is useful for obtaining information of thermomagnetic phase transitions, such as Curie temperature, critical exponents (even in biphasic systems), order of the phase transition and critical composition for which rst order phase transition becomes second order. These analyses were performed in well know materials such as Gd, Gd5Si2Ge2, La(Fe,Si)13, Ni-Mn-In Heusler alloys and Fe-, Co-, Ni-amorphous and nanocrystalline alloys. Next, various possible avenues to optimize the magnetocaloric behavior by tapping on the characteristics of rst and second order phase transition type systems were investigated. For second order phase transition type, the coe cient of refrigerant performance was optimized as a function of the amount of the various phase fractions in Gd-GdZn composite, while an enhanced magnetic eld responsiveness is achived in nanostructured Gd/Ti multilayers. For rst order phase transition type, reduction of hysteresis and enhancement of rst order character is achieved in Ni- and Cr-doped La(Fe,Si)13 compounds, respectively.Esta tesis se centra en el análisis de las relaciones entre las transiciones de fase termomagnéticas y la respuesta magnetocalórica de los materiales. En primer lugar,se han estudiado diferentes factores experimentales que pueden afectar a la medida e interpretacióndel efecto magnetocalórico, como son: la geometría de la muestra, la presencia de inhomogeneidades composicionales, el truncado de datos calorimétricos a bajas temperaturas y los protocolos de medida para la caracterización directa del efecto magnetocalórico. Posteriormente, se ha puesto de manifiesto que el análisis de la dependencia del efecto magnetocalórico con el campo magnético sirve para obtener información de las transiciones de fase termomagnéticas tales como la temperatura de Curie, los exponentes críticos y el orden de la transición, así como la composición crítica a la queel sistema transita de una transición de fase deprimer orden a una desegundo orden. Estos análisis se han llevado a cabo en materiales ampliamente conocidos tales como Gd, Gd5Si2Ge2, La(Fe,Si)13, aleaciones Heusler Ni-Mn-In y aleaciones amorfas y nanocristalinas basadas en Fe, Co y Ni. Finalmente, se han investigado varias rutas para la optimización de las propiedades magnetocalóricas de los materiales aprovechando las características de las transiciones de primero y segundo orden. Para las transiciones de segundo orden, se ha optimizado la capacidad de refrigeración en función de la fracción de fasesen compuestos Gd-GdZn.Para multicapas nanoestructuradas de Gd/Ti, se ha encontrado una mejor respuesta al campo magnético. Para las transiciones de primer orden, en compuestos La(Fe,Si)13 dopados con metales de transición,se ha reducido la histéresis asociada a la transición mediante el dopado con Ni y se ha aumentado el carácter de primer orden de la transición mediante la adición de Cr. Para estos estudios se han utilizado los métodos de análisis previamente tratados.Premio Extraordinario de Doctorado U

Setting the basis for the interpretation of temperature first order reversal curve (TFORC) distributions of magnetocaloric materials

First Order Reversal Curve (FORC) distributions of magnetic materials are a well-known tool to extract information about hysteresis sources and magnetic interactions, or to fingerprint them. Recently, a temperature variant of this analysis technique (Temperature-FORC, TFORC) has been used for the analysis of the thermal hysteresis associated with first-order magnetocaloric materials. However, the theory supporting the interpretation of the diagrams is still lacking, limiting TFORC to a fingerprinting technique so far. This work is a first approach to correlate the modeling of first-order phase transitions, using the Bean–Rodbell model combined with a phenomenological transformation mechanism, with the features observed in experimental TFORC distributions of magnetocaloric materials. The different characteristics of the transformations, e.g., transition temperatures, symmetry, temperature range, etc., are correlated to distinct features of the distributions. We show a catalogue of characteristic TFORC distributions for magnetocaloric materials that exhibit some of the features observed experimentally.Army Research Laboratory W911NF-19-2-021

Reversibility of the Magnetocaloric Effect in the Bean-Rodbell Model

The applicability of magnetocaloric materials is limited by irreversibility. In this work, we evaluate the reversible magnetocaloric response associated with magnetoelastic transitions in the framework of the Bean-Rodbell model. This model allows the description of both second- and first-order magnetoelastic transitions by the modification of the η parameter (η1 for first-order ones). The response is quantified via the Temperature-averaged Entropy Change (TEC), which has been shown to be an easy and effective figure of merit for magnetocaloric materials. A strong magnetic field dependence of TEC is found for first-order transitions, having a significant increase when the magnetic field is large enough to overcome the thermal hysteresis of the material observed at zero field. This field value, as well as the magnetic field evolution of the transition temperature, strongly depend on the atomic magnetic moment of the material. For a moderate magnetic field change of 2 T, first-order transitions with η≈1.3−1.8 have better TEC than those corresponding to stronger first-order transitions and even second-order ones.Universidad de Sevilla US-1260179Junta de Andalucía P18-RT-746Army Research Laboratory W911NF192021

Influence of Thermal and Magnetic History on Direct DTad Measurements of Ni49+xMn36-xIn15 Heusler Alloys

In the present work, using Heusler Ni49+xMn36-xIn15 (with x = 0 and 0.5) alloys, it is shown that the choice of the appropriate measurement protocol (erasing the prior state of the sample in between experiments) in DTad first shot characterization is crucial for obtaining reliable results. Unlike indirect measurements, for which incorrect protocols produce overestimates of the characteristics of the material, erroneous direct measurements underestimate DTad in the region close to its first order phase transition. The error in DTad is found to be dependent on the temperature step used, being up to ~40% underestimation, including a slight shift in its peak temperature.AEI/FEDER-UE (project MAT-2016-77265-R)US Army Research Laboratory W911NF-19-2-021

Alimentos funcionales para cerdos al destete

A functional food is a compound that, being or not a nutrient, has a positive effect on one or several functions in the organism, producing well-being in the animal. The following compounds are considered functional foods: prebiotics, probiotics, symbiotics, antioxidants, secondary products of plant metabolism, structural lipids, polyunsaturated fatty acids, fat metabolism byproducts, bioactive peptides, fi ber, vitamins and minerals. Prebiotics, probiotics and symbiotics are modifi ers of the intestinal microfl ora increasing mainly lactobacilli and bifi dobacteria populations and reducing pathogenic bacteria. Lactobacilli and bifi - dobacteria use oligosaccharides and fructo-oligosaccharides arriving at the colon, producing fatty acids and freeing minerals to be absorbed and utilized by the host. Prebiotics are partially-digestible oligosaccharides; probiotics are microorganisms (mainly lactobacilli and bifi dobacteria); and symbiotics are a mixture of probiotics and prebiotics. During the weaning period, piglets face dramatic changes in feeding management and environment, affecting feed intake and, at the same time, affecting digestive functions resulting in lower growth and higher incidence of disease, mainly diarrhea. Functional food may be an alternative to reduce the effects of weaning on growth performance and health of piglets, to diminish or to avoid gastrointestinal problems during weaning, preventing the proliferation of pathogenic bacteria, and improving digestive functions. All these may help to withdraw antibiotics from piglet feed

Nanostructuring as a procedure to control the field dependence of the magnetocaloric effect

In this work, the field dependence of the magnetocaloric effect of Gd bulk samples has been enhanced through nanostructuring of the material. Nanostructuring consists in multilayers preparation by alternative rf-sputtering deposition of Gd layers and Ti spacers onto glass substrates. The results obtained for the multilayers were compared to those obtained for the Gd bulk. Assuming a power law for the field dependence of the magnetic entropy change (ΔSM ∝ Hn ), higher field dependences close to the transition in a wider temperature range are obtained for the multilayer material (n = 1.0) with respect to the bulk counterpart (n = 0.78). The effect of a Curie temperature distribution in the multilayer material (due to variations of the layer thickness) has been studied through numerical simulations to explain the observed field dependence of the magnetocaloric effect, obtaining a remarkable agreement between experiments and results.Ministerio de Economía y Competitividad español y EU-FEDER. MAT2013-45165-P y MAT2016-77265-RMinistry of Education and Science of the Russian Federation. Project No. 258

EXPRO: exoesqueleto para rehabilitación de miembro superior

In the upper limb rehabilitation field, assisting to various patients per day, in different kinds of therapies is an exhausting task which can be achieved in a semiautomated or automated manner.  The ExPro is an exoskeleton of 3 degrees of freedom designed and created to support rehabilitation treatments for patients with little or no mobility in their arms. The device consists in a machine able to move forearm and wrist according to prone-supination, ulnar and radial deflection and flex-extension of wrist movements. The proposed prototype was designed to assist therapists in the first step of rehabilitation treatments, thus, passive therapies. Each mechanical component was designed in the Inventor 3D software and printed on PLA materials (polylactic acid). The controlling step is a Raspberry Pi 3 that receives information, interprets and connects power, and control PCBs. The design and calculations were tasted with the finite elements tool of inventor software. The work result presents an exoskeleton prototype easy to operate and transport, safe for the patient and able to carry out several preprogramed movements.En el campo de la rehabilitación, asistir a varios pacientes por día en diferentes tipos de terapias es una tarea extenuante que puede ser llevada a cabo de manera semiautomatizado o automatizada. El ExPro es un exoesqueleto de tres grados de libertad diseñado y construido para asistir tratamientos de rehabilitación en pacientes con poca o nula movilidad en sus brazos. El dispositivo consiste en una máquina capaz de mover el antebrazo y la muñeca acorde a los movimientos de pronosupinación, flexión ulnar y radial y flexo-extensión de muñeca

Oral Calcidiol Is More Effective Than Cholecalciferol Supplementation to Reach Adequate 25(OH)D Levels in Patients with Autoimmune Diseases Chronically Treated with Low Doses of Glucocorticoids: A "Real-Life" Study

Glucocorticoids (GCs) are the cornerstone of the therapy in many autoimmune and inflammatory diseases. However, it is well known that their use is a double edged sword, as their beneficial effects are associated almost universally with unwanted effects, as, for example glucocorticoid-induced osteoporosis (GIO). Over the last years, several clinical practice guidelines emphasize the need of preventing bone mass loss and reduce the incidence of fractures associated with GC use. Calcium and vitamin D supplementation, as adjunctive therapy, are included in all the practice guidelines. However, no standard vitamin D dose has been established. Several studies with postmenopausal women show that maintaining the levels above 30-33 ng/mL help improve the response to bisphosphonates. It is unknown if the response is the same in GIO, but in the clinical practice the levels are maintained at around the same values. In this study we demonstrate that patients with autoimmune diseases, undergoing glucocorticoid therapy, often present suboptimal 25(OH)D levels. Patients with higher body mass index and those receiving higher doses of glucocorticoids are at increased risk of having lower levels of 25(OH)D. In these patients, calcidiol supplementations are more effective than cholecalciferol to reach adequate 25(OH)D levels

Microconformado de Materiales Metálicos mediante Pulsos Láser en el Dominio de ns

La demanda de miniaturización introducida, entre otros, por la industria de fabricación de MEMS (Micro Electro Mechanical Systems), hace necesario caracterizar y validar los procesos que emplean el láser en el microconformado de materiales metálicos a escala submilimétrica. Como alternativa al microconformado térmico, que hace uso de las deformaciones de origen térmico inducidas por la radiación láser, el microconformado mediante pulsos láser en el dominio de ns hace posible el conformado de materiales metálicos manteniendo, o incluso mejorando, las propiedades mecánicas de los mismos debido a la inducción de tensiones residuales de compresión en la superficie de la pieza tratada. Se presenta en este trabajo el estudio teórico y experimental del microconformado láser mediante la caracterización de diversas pruebas elementales. Miniaturization of components demanded by MEMS (Micro Electro Mechanical Systems) industry, makes necessary the validation of the manufacturing processes applied to submillimetric metallic materials in which laser is used. As an alternative to thermal microforming in which laser induced thermal fields are responsible for the forming phenomena, the use of ns laser pulses makes possible microforming of metallic materials preserving, or even improving, their mechanical properties, due to the induction of residual stresses in the surface. In the present paper experimental tests and FEM simulation results on nanosecond time scale laser microforming are presented