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The present study investigates the influence of iron (Fe) doping on the martensitic transformation and magnetic properties of Ni50−xMn37Sn13Fex(x = 0.5, 1, 1.5) magnetic shape memory alloys in ribbon form. The ribbons were prepared using arc-melting followed by melt-spinning processes and were characterized using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and vibrating sample magnetometry. Our findings demonstrate that the addition of Fe shifts the martensitic transformation to lower temperatures and increases the Curie point of the austenitic phase, T c A , leading to an enhanced magnetism in the austenitic phase. Moreover, a significant increase in the magnetization jump (Δ M) is observed, from 3.3 emu\ g - 1 for x = 1 to 17 emu\ g - 1 for x = 1.5 under a 50 Oe applied magnetic field. The structural transformations are also found to be sensitive to the external applied magnetic field. The isothermal magnetization curves exhibit the exchange bias effect, which confirms the coexistence of antiferromagnetic and ferromagnetic coupling in the samples. Furthermore, the exchange bias effect increases with the Fe content. [ABSTRACT FROM AUTHOR]

It is known that Co substitution in magnetic shape memory Ni-Mn-Sn alloys produces changes in their thermomagnetic behaviour. In this work, the Ni49Co1 Mn37Sn13 alloy was obtained by melt spinning in ribbon shape. The ribbon flakes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and differential scanning calorimetry (DSC). SEM micrographs indicate the formation of textured ribbons with columnar grains growing up perpendicular to the ribbons plane. The crystallographic structure of the sample at room temperature is the Heusler L21. DSC cyclic scans reveal the martensitic transformation on cooling and the reverse austenitic transformation on heating below room temperature. The application of a magnetic field produces a decrease in the transformation temperatures. The small amount of Co addition increases the Curie temperature of austenite. These facts suggest that the structural and magnetic phase transformation temperatures of the ribbons could be tuned to the desired functional temperature by controlling the applied magnetic field as well as the cobalt amount. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

It is known that Co substitution in magnetic shape memory Ni-Mn-Sn alloys produces changes in their thermomagnetic behaviour. In this work, the Ni49Co1 Mn37Sn13 alloy was obtained by melt spinning in ribbon shape. The ribbon flakes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and differential scanning calorimetry (DSC). SEM micrographs indicate the formation of textured ribbons with columnar grains growing up perpendicular to the ribbons plane. The crystallographic structure of the sample at room temperature is the Heusler L21. DSC cyclic scans reveal the martensitic transformation on cooling and the reverse austenitic transformation on heating below room temperature. The application of a magnetic field produces a decrease in the transformation temperatures. The small amount of Co addition increases the Curie temperature of austenite. These facts suggest that the structural and magnetic phase transformation temperatures of the ribbons could be tuned to the desired functional temperature by controlling the applied magnetic field as well as the cobalt amount. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: The structural evolution and the phase transformations occurred during milling process of Co100−x Cr x (x =0, 20, 50) alloys are investigated by X-ray diffraction. Microstructural parameters such as the crystallites size, the microstrains, the stacking faults, the dislocation density and the phase fraction were determined from the Rietveld refinement of the X-ray diffraction patterns. The results show the formation of nanostructured alloys which depend on the initial composition of the mixture. In addition, X-ray diffraction indicates that the ball milling induces the fcc to hcp phase transformation in the first stage of milling and the reverse hcp to fcc phase transformation at the end of milling. On the basis of Warren''s model, these allotropic transformations were explained by the presence of dislocations and the accumulation of stacking faults in the hcp and the fcc structures. [Copyright &y& Elsevier]

Abstract: The ball milling of blended chromium and cobalt powders was carried out in a planetary mill in order to obtain a nanostructured Cr20Co80 alloy. The structural modifications at different stages of the ball milling are investigated with X-ray diffraction. Several microstructure parameters such as the crystallite size, microstrains, stacking faults, dislocation density and phase fractions are determined. As the milling proceeded, the chromium peaks disappeared progressively indicating the dissolution of the chromium atoms into the cobalt matrix. Disordered hcp-Co(Cr) and fcc-Co(Cr) solid solutions were formed after 24h of milling. The hcp solid solution has a lower value of the crystallite size and a higher degree of microstrains and dislocation density than the fcc solid solution. For prolonged milling (48h), plastic deformations introduce large amounts of stacking faults in the hcp structure leading to the reverse hcp–fcc transformation of the Co(Cr) solid solution. The kinetic parameters n =0.81 and k =0.11, obtained using the Johnson–Mehl–Avrami formalism, correspond to diffusion mechanisms through interfaces and dislocations. [Copyright &y& Elsevier]