15 research outputs found
Martensitic transformation, magnetic and magnetocaloric properties of NiâMnâFeâSn Heusler ribbons
Melt-spun ribbons of nominal composition Ni50Mn36-xFexSn14 (x = 0, 2, and 3) were prepared by melt-spinning. The alloys undergo a martensitic transformation from L21 austenite to an orthorhombic 4O martensite on cooling, as determined by X-ray powder diffraction analysis. Replacement of Mn by Fe linearly reduces the characteristic temperatures of the martensitic transformation (the equilibrium temperature decreases from 328 to 285 K) and reduces the Curie temperature of the austenite phase (from 336 to 300 K), whereas the effect of the applied magnetic field on the martensite transition temperatures is negligible. Magnetic measurements (zero-field cooled, ZFC, and field cooled, FC, curves, AC susceptibility measurements) hint the coexistence of two different ferromagnetic martensitic magnetic phases. Moreover, the AC susceptibility measurements and the irreversibility of the ZFC and FC curves point towards the presence of antiferromagnetic and ferromagnetic interactions in the martensitic phase. All samples exhibit spontaneous exchange bias at 2 K, with double-shifted loops, whereas the evolution of the conventional exchange bias with the temperature agrees quite well with the behavior of ferromagnetic regions surrounded by spin-glass regions or with the coexistence of ferromagneticâantiferromagnetic interactions. Ni50Mn36-xFexSn14 ribbons present a moderate inverse magnetocaloric effect (with a maximum of the magnetic entropy change of 5.7 Jkgâ1Kâ1 for ÎŒ0H = 3 T for x = 3). It is worth to note that these materials feature a significant reservoir (up to 44 Jkgâ1Kâ1 for x = 2) of magnetic entropy change, linked to the proximity of the austenitic ferromagnetic transition to the martensitic transformation.Se prepararon cintas hiladas por fusiĂłn de composiciĂłn nominal Ni 50 Mn 36-x Fe x Sn 14 (x = 0, 2 y 3) mediante hilatura por fusiĂłn. Las aleaciones experimentan una transformaciĂłn martensĂtica de austenita L2 1 a una martensita ortorrĂłmbica 4O al enfriarse, segĂșn lo determinado por anĂĄlisis de difracciĂłn de rayos X en polvo. La sustituciĂłn de Mn por Fe reduce linealmente las temperaturas caracterĂsticas de la transformaciĂłn martensĂtica (la temperatura de equilibrio desciende de 328 a 285 K) y reduce la temperatura de Curie de la fase austenita (de 336 a 300 K), mientras que el efecto del campo magnĂ©tico aplicado sobre las temperaturas de transiciĂłn martensĂtica es despreciable. Las mediciones magnĂ©ticas (campo cero enfriado, ZFC y campo enfriado, FC, curvas, medidas de susceptibilidad de CA) sugieren la coexistencia de dos fases magnĂ©ticas martensĂticas ferromagnĂ©ticas diferentes. AdemĂĄs, las medidas de susceptibilidad AC y la irreversibilidad de las curvas ZFC y FC apuntan hacia la presencia de interacciones antiferromagnĂ©ticas y ferromagnĂ©ticas en la fase martensĂtica. Todas las muestras exhiben un sesgo de intercambio espontĂĄneo a 2 K, con bucles de doble desplazamiento, mientras que la evoluciĂłn del sesgo de intercambio convencional con la temperatura concuerda bastante bien con el comportamiento de regiones ferromagnĂ©ticas rodeadas por regiones spin-glass o con la coexistencia de interacciones ferromagnĂ©ticas-antiferromagnĂ©ticas. Ni50 Mn 36-x Fe x Sn 14 Las cintas presentan un efecto magnetocalĂłrico inverso moderado (con un cambio de entropĂa magnĂ©tica mĂĄximo de 5,7 Jkg â1 K â1 para ÎŒ 0 H = 3 T para x = 3). Vale la pena señalar que estos materiales presentan un reservorio significativo (hasta 44 Jkg â1 K â1 para x = 2) de cambio de entropĂa magnĂ©tica, vinculado a la proximidad de la transiciĂłn ferromagnĂ©tica austenĂtica a la transformaciĂłn martensĂtica
Effect of the Boron Content on the Amorphization Process and Magnetic Properties of the Mechanically Alloyed Fe92âxNb8Bx Powders
Thermal and structural study of nanocrystalline Fe(Co)NiZrB alloys prepared by mechanical alloying
Structural, Thermal and Magnetic Properties of Nanocrystalline Co80Ni20 Alloy Prepared by Mechanical Alloying
Elaboration, Microstructure, and Magnetic Properties of Nanocrystalline Fe90Ni10 Powders
Formation and Magnetic Properties of Nanocomposites in Rapidly Solidified Fe42Ni41.7C7Si4.5B3.9P0.9 (at%) Ribbons
Studies of crystallization kinetics in a-Se80âxTe20Cdx and a-Se80âxTe20Gex alloys using D.C. conductivity measurements
Thermal Stability Investigation and the Kinetic Study of FolnakÂź Degradation Process Under Nonisothermal Conditions
The nonisothermal degradation process of FolnakÂź drug samples was investigated by simultaneous thermogravimetric and differential thermal analysis in the temperature range from an ambient one up to 810°C. It was established that the degradation proceeds through the five degradation stages (designated as I, II, III, IV, and V), which include: the dehydration (I), the melting process of excipients (II), as well as the decomposition of folic acid (III), corn starch (IV), and saccharose (V), respectively. It was established that the presented excipients show a different behavior from that of the pure materials. During degradation, all excipients increase their thermal stability, and some kind of solidâsolid and/or solidâgas interaction occurs. The kinetic parameters and reaction mechanism for the folic acid decomposition were established using different calculation procedures. It was concluded that the folic acid decomposition mechanism cannot be explained by the simple reaction order (ROn) model (nâ=â1) but with the complex reaction mechanism which includes the higher reaction orders (RO, nâ>â1), with average value of <nâ>â=â1.91. The isothermal predictions of the third (III) degradation stage of FolnakÂź sample, at four different temperatures (Tisoâ=â180°C, 200°C, 220°C, and 260°C), were established. It was concluded that the shapes of the isothermal conversion curves at lower temperatures (180â200°C) were similar, whereas became more complex with further temperature increase due to the pterin and p-amino benzoic acid decomposition behavior, which brings the additional complexity in the overall folic acid decomposition process