Caloric effects around phase transitions in magnetic materials described by ab initio theory : the electronic glue and fluctuating local moments

We describe magneto-, baro-, and elastocaloric effects (MCEs, BCEs, and eCEs) in materials, which possess both discontinuous (first-order) and continuous (second-order) magnetic phase transitions. Our ab initio theory of the interacting electrons of materials in terms of disordered local moments has produced explicit mechanisms for the drivers of these transitions, and here, we study associated caloric effects in three case studies where both types of transition are evident. Our earlier work had described FeRh’s magnetic phase diagram and large MCE. Here, we present calculations of its substantial BCE and eCE. We describe the MCE of dysprosium and find very good agreement with experimental values for isothermal entropy ((ΔSiso) and adiabatic temperature (ΔTad) changes over a large temperature span and different applied magnetic field values. We examine the conditions for optimal values of both ΔSiso and ΔTad that comply with a Clausius–Clapeyron analysis, which we use to propose a promising elastocaloric cooling cycle arising from the unusual dependence of the entropy on temperature and biaxial strain found in our third case study—the Mn3GaN antiperovskite. We explain how both ΔSiso and ΔTad can be kept large by exploiting the complex tensile strain–temperature magnetic phase diagram, which we had earlier predicted for this material and also propose that hysteresis effects will be absent from half of the caloric cycle. This rich and complex behavior stems from the frustrated nature of the interactions among the Mn local moments

First-order ferromagnetic transitions of lanthanide local moments in divalent compounds: An itinerant electron positive feedback mechanism and Fermi surface topological change

Around discontinuous (first-order) magnetic phase transitions the strong caloric response of materials to the application of small fields is widely studied for the development of solid-state refrigeration. Typically strong magnetostructural coupling drives such transitions and the attendant substantial hysteresis dramatically reduces the cooling performance. In this context we describe a purely electronic mechanism which pilots a first-order paramagnetic-ferromagnetic transition in divalent lanthanide compounds and which explains the giant non-hysteretic magnetocaloric effect recently discovered in a Eu$_2$In compound. There is positive feedback between the magnetism of itinerant valence electrons and the ferromagnetic ordering of local $f$-electron moments, which appears as a topological change to the Fermi surface. The origin of this electronic mechanism stems directly from Eu's divalency, which explains the absence of a similar discontinuous transition in Gd$_2$In.Comment: 8 pages, 7 figure

Theory of magnetic ordering in the heavy rare earths : ab initio electronic origin of pair- and four-spin interactions

We describe a disordered local moment theory for long-period magnetic phases and investigate the temperature and magnetic field dependence of the magnetic states in the heavy rare earth elements (HREs), namely, paramagnetic, conical and helical antiferromagnetic (HAFM), fan, and ferromagnetic (FM) states. We obtain a generic HRE magnetic phase diagram which is consequent on the response of the common HRE valence electronic structure to f-electron magnetic moment ordering. The theory directly links the first-order HAFM-FM transition to the loss of Fermi surface nesting, induced by this magnetic ordering, as well as provides a template for analyzing the other phases and exposing where f-electron correlation effects are particularly intricate. Gadolinium, for a range of hexagonal, close-packed lattice constants c and a, is the prototype, described ab initio, and applications to other HREs are made straightforwardly by scaling the effective pair and quartic local moment interactions that emerge naturally from the theory with de Gennes factors and choosing appropriate lanthanide-contracted c and a values

IN VITRO DETERMINATION OF MINIMUM LENGTH PENETRATION OF A 27G MONOJECT NEEDLE TO IRRIGATE THE MAIN CANAL, AVOIDING EXTRUSION

Objective: To determine the minimum length penetration required of a monoject27G needle to irrigate the main canal, avoiding extrusion. Materials and methods: 52 teeth were used, decoronated and worked at equal lengths at a MAF 40. They were randomly assembled in 3 molds and irrigated with diluted Omnipaque. Central trend values were calculated using descriptive statistics. Barlett, Shapiro Wilk and ANOVA one-way tests were applied to analyze statistically significant differences. Subsequently the logistic regression of Oswell-Lemeshow was calculated to look for causality between variables. Results: Statistically significant results show that at higher needle penetration, the probability of extrusion is greater; regarding minimal length penetration to prevent extrusion, the safest length to irrigate is working length (WL) -4mm. Conclusions: The minimum length penetration to irrigate preventing extrusion is WL-4 mm

Habitando la casa invisible

Universidad Pablo de OlavideMinisterio de Ciencia e Innovación CSO2009-06819-EUniversidad de Granada 1975-200

Towards better concordance among contextualized evaluations in FAST-GDM problems

A flexible attribute-set group decision-making (FAST-GDM) problem consists in finding the most suitable option(s) out of the options under consideration, with a general agreement among a heterogeneous group of experts who can focus on different attributes to evaluate those options. An open challenge in FAST-GDM problems is to design consensus reaching processes (CRPs) by which the participants can perform evaluations with a high level of consensus. To address this challenge, a novel algorithm for reaching consensus is proposed in this paper. By means of the algorithm, called FAST-CR-XMIS, a participant can reconsider his/her evaluations after studying the most influential samples that have been shared by others through contextualized evaluations. Since exchanging those samples may make participants’ understandings more like each other, an increase of the level of consensus is expected. A simulation of a CRP where contextualized evaluations of newswire stories are characterized as augmented intuitionistic fuzzy sets (AIFS) shows how FAST-CR-XMIS can increase the level of consensus among the participants during the CRP