Magnetic properties of the complex concentrated alloy system CoFeNi0.5Cr0.5Alx

We study the change in magnetisation with paramagnetic Al addition in the CoFeNi0.5Cr0.5–Alx (x: 0, 0.5, 1, and 1.5) complex concentrated alloy. The compositions were developed utilising the Mulliken electronegativity and d-electron/atom ratio. Spherical FeCr rich nanoprecipitates are observed for X: 1.0 and 1.5 in an AlCoNi-rich matrix. A ~ 5 × increase in magnetisation (from 22 to 96 Am2/kg) coincides with this nanoprecipitate formation—the main magnetic contribution is determined to be from FeCr nanoprecipitates. The magnetisation increase is strange as paramagnetic Al addition dilutes the ferromagnetic Fe/Co/Ni additions. In this paper we discuss the magnetic and structural characterisation of the CoFeNi0.5Cr0.5–Alx composition and attempt to relate it to the interfacial energy

Investigation into the magnetic properties of CoFeNiCryCux alloys

The search for cheap, corrosion-resistant, thermally-mechanically stable functional magnetic materials, including soft magnetic and magneto-caloric materials has led to research focused on high entropy alloys (HEAs). Previous research shows that alloying elements with negative enthalpies of mixing can facilitate a second-order phase transition. On the other side of the spectrum, compositional segregation cause by positive enthalpy of mixing alloying additions (such as Cu) may also be used to tune magnetic properties. This paper studies the structural, magnetic and magneto-caloric effect of the FCC alloys CoFeNiCryCux (x = 0.0, 0.5, 1.0 and 1.5, y = 0.0, 0.8 and 1.0) to tune these properties with Cu and Cr alloying. Scanning electron microscopy of the compositions show nanoparticles forming within the grains as the Cu concentration increases. Cr addition to CoFeNiCu1.0 has a larger effect on the magnetic and magneto-caloric properties compared to the Cu addition to CoFeNiCr1.0. The addition of Cu (x = 0.5) to CoFeNiCr1.0 improved both the saturation magnetisation and Curie temperature; addition of Cr (y = 1.0) to CoFeNiCu1.0 decreased the Curie temperature by 900 K. All alloys were determined to have a second-order phase transition around their Curie temperature. The refrigerant capacity at 2 T was found to be similar to existing HEAs, although the Curie temperatures were lower than room temperature. Based on this data the CoFeNiCr0.8Cu composition was fabricated to increase the Curie temperature towards 300 K to explore these HEAs as new candidates for room temperature magneto-caloric applications. The fabricated composition showed Curie temperature, saturation magnetisation, and refrigerant capacity increasing with the small reduction in Cr content

La Construcción del Conocimiento como Proceso Activo en la Enseñanza

This paper is related with the historical development of pedagogical sciences in active education. Basically is showed the hypothesis that a better education is this one where the knowledge is build by the student, having these an active position in his own education, decreasing the passivity or listening and memorizing professors conferences. It wasn't until the ends of XIX century, when pedagogic was considered an independent science of knowledge, before, from ancient, we found ideas respect the teaching method as a part of the predominant philosophy in every region and epoch, and really closed to the interesting of religion and state.Este trabajo intenta realizar un recorrido en la historia de la pedagogía, básicamente resaltando aquellos intentos que con mayor o menor resultados planteaban la hipótesis de que una mejor educación es aquella en la que el conocimiento se construye por el estudiante, al tener este una posición activa en su propia educación, disminuyendo la pasividad de escuchar y memorizar las conferencias de los profesores. No es sino hasta finales del siglo XIX cuando la pedagogía se considera una rama independiente del saber, anteriormente, desde la antigüedad, encontramos ideas respecto al método de enseñanza como parte de la filosofía predominante en cada región y época, y ampliamente sujeta a los intereses de la religión y el estado

On the structural, microstructural and magnetic properties evolution of Ni0.5FeCoAlCrx alloys

The multicomponent alloy CoFeNiAlCr has shown great promise as a soft magnetic material due to its small coercive field and high saturation magnetisation at room temperature. By changing the ratio of the components, the Curie temperature can be tuned, along with improvements in both the coercive field and saturation magnetisation. The alloy system is interesting as the ratio of Al to Cr determines whether a single solid phase or a dual phase alloy is formed. This work has investigated the effects of Cr addition on the structural and magnetic properties of CoFeNi0.5AlCrx. It discusses the evolution of the NPs-matrix segregations and its constituents’ phases

On the correct estimation of the magnetic entropy change across the magneto-structural transition from the Maxwell relation: Study of MnCoGeBx alloy ribbons

An accurate calculation of the different magnetocaloric-related magnitudes derived from the temperature dependence of the magnetic entropy change in materials exhibiting first-order magnetocaloric effect is imperative to correctly estimate the true potential of a specific material for refrigeration purposes. In this contribution, we present a meticulous study of two different thermal procedures to measure the set of isothermal magnetization curves from which the total field induced magnetic entropy change, ΔST, is calculated using the adequate Maxwell relation. If the accurate determination of ΔST for any temperature is pursued the thermal and magnetic history of the materials must be taken into account, and then, the unidirectional measurement of reversible isothermal magnetization curves after a thermal cycle is required. The analysis was conducted on MnCoGeB0.01 alloy ribbons that show a giant ΔST at the coupled magneto-structural transition, from a ferromagnetic (TiNiSi-type) phase to a paramagnetic (NiIn2-type) one, owing to the concomitant abrupt magnetization change. We suggest that the conclusions reached can be applicable to any other system displaying magnetocaloric effect originated at a first-order phase transition

Expanded use of a fast photography technique to characterize laser-induced plasma plumes

Expanded use of fast photography is proposed to characterize laser ablation plasma plumes by the analysis of a set of photographs by means of appropriate mathematical algorithms. The laser ablation plasma plumes studied were generated by ablation of both a multicomponent target of the nominal composition Ni50Mn37Sn13 and a highly pure Cu target (Cu) using a Q-switched Nd-YAG laser system:The experiments were conducted under different background argon pressures. Several photograph parameters such as intensity per unit time of exposure for a pixel, mean intensity per pixel per unit time of exposure, integrated intensity and cross correlation were studied. The intensity per unit time of exposure allowed for identification of the fast component of the triple structure of the expanding plasma into the background gas (that travels at a speed close to the one measured in vacuum). This parameter together with the use of cross correlation enabled the identification of regions of the expanded plasma plume with higher and lower similarities in their optical emission behavior. The mean intensity per pixel per unit time of exposure can be used as a measurement of the amount of light emitted by the plume as a function of time