Heusler alloy Mn 50 Ni 40 In 10 was produced as preferentially textured ribbon flakes by melt spinning, finding the existence of martensitic-austenic transformation with both phases exhibiting ferromagnetic ordering. A microcrystalline three-layered microstructure of ordered columnar grains grown perpendicularly to ribbon plane was formed between two thin layers of smaller grains. The characteristic temperatures of the martensitic transformation were M S = 213 K, M f = 173 K, A S = 222 K, and A f = 243 K. Austenite phase shows a cubic L2 1 structure ͑a = 0.6013͑3͒ nm at 298 K and a Curie point of 311 K͒, transforming into a modulated fourteen-layer modulation monoclinic martensite. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2827179͔Since Sutou et al.1 reported the occurrence of martensitic transformation in the ferromagnetic Heusler system Ni 50 Mn 50−x In x , considerable attention has been dedicated to study magnetism and magnetic shape memory effect, [2][3][4] magnetic entropy change, [4][5][6][7][8] and magnetotransport properties 9-11 of these alloys. Nevertheless, ferromagnetism in both phases is only observed in the narrow composition range of 15ഛ x ഛ 16 2 . The characteristic temperatures of the reversible first order structural transformation between both phases, referred as martensitic and austenitic starting and finish temperatures ͑i.e., M S , M f , A S , and A f , respectively͒, strongly vary upon small changes in the chemical composition. The crystal structure of austenite and martensite depends on the composition, 2,4 and the transformation can be also induced by applying a magnetic field.2-4 Additionally, a large inverse and direct magnetocaloric effect has been measured in Ni 50 Mn 34 In 16 .6-8 Ni-Mn-In Heusler alloys are therefore of significant prospective importance for applications in both magnetically driven actuators due to magnetic shape memory effect and as working substances in magnetic refrigeration technology.Until now, the investigated alloys are usually bulk polycrystals obtained by arc or induction melting followed by a high temperature annealing, [1][2][3][4][5][6][7][8]10 or single crystals grown by Czochralski method.9,11 Present investigation was carried out to employ rapid quenching by melt spinning to produce MnNi-In Heusler alloys. This technique offers two potential advantages for the fabrication of these magnetic shape memory alloys: the avoiding, or reduction, of the annealing to reach a homogeneous single phase alloy, and the synthesis of highly textured polycrystalline ribbons. Ribbon shape can be also appropriate for use in practical devices. We fabricated the alloy Mn 50 Ni 40 In 10 by melt spinning. Its valence electronic concentration per atom e / a is 7.801, allowing the existence of martensite-austenite transformation with both phases exhibiting ferromagnetic ordering, opening its potential use as a magnetic shape memory alloy. 3 We report in this letter a preliminary characterization of the microstructural features and magnetic behavior.As-cast pel...

The Heusler alloy Ni 50 Mn 37 Sn 13 was successfully produced as ribbon flakes of thickness around 7-10 m melt spinning. Fracture cross section micrographs in the ribbon show the formation of a microcrystalline columnarlike microstructure, with their longer axes perpendicular to the ribbon plane. Phase transition temperatures of the martensite-austenite transformation were found to be M S = 218 K, M f = 207 K, A S = 224 K, and A f = 232 K; the thermal hysteresis of the transformation is 15 K. Ferromagnetic L2 1 bcc austenite phase shows a Curie point of 313 K, with cell parameter a = 0.5971͑5͒ nm at 298 K, transforming into a modulated 7M orthorhombic martensite with a = 0.6121͑7͒ nm, b = 0.6058͑8͒ nm, and c = 0.5660͑2͒ nm, at 150 K. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2832330͔Ferromagnetic shape memory alloys ͑FSMA͒ are of considerable interest because of their exceptional magnetoelastic properties.1-3 The shape memory effect can not only be controlled by changing the temperature, as it occurs in traditional shape memory alloys, but also by varying the magnetic field up to moderate field values. The latter makes them of noteworthy interest for developing new thermal or magnetically driven actuators. 4Among the Heusler alloys that exhibit magnetic shape memory effect, the most extensively studied are those of the Ni-Mn-Ga system. However, to overcome some of the problems related to practical application, such as the high cost of gallium and the low martensitic transformation temperature that they usually present, the search for Ga-free alloys has been recently attempted. Martensitic transformation in ferromagnetic Heusler Ni 50 Mn 50−x Sn x alloys with 10ഛ x ഛ 16.5 was first reported by Sutou et al. 5 Later, Krenke et al. studied phase transformations and magnetic and magnetocaloric properties of the Ni 50 Mn 50−x Sn x alloy series with 5 ഛ x ഛ 25. 6,7 Samples with x = 0.13 and 0.15 are ferromagnetic in the martensitic state undergoing a first order martensitic-austenitic structural transition at a temperature below the respective Curie points of both phases. At room temperature, the alloy with x = 0.13 is martensitic, and the martensite-austenite transformation occurs around room temperature. Brown et al. 8 12 They report magnetic entropy changes up to 10.4 J / kg K at 10 kOe for x = 7. Ni-Mn-Sn system is, therefore, of prospective importance as FSMA and as promising magnetic refrigerant alloy. In all these cases, alloys were produced as bulk polycrystalline samples.In this work we produced, as far as we know for the first time, Ni-Mn-Sn alloys by rapid solidification. This procedure offers several potential advantages for the fabrication of the shape memory materials such as avoiding the homogenization annealing step to reach a single phase alloy and the synthesis of highly textured polycrystalline samples. Moreover, ribbon shape is appropriate for direct use in practical devices. In view of its interesting properties, 6,7 we have selected the alloy Ni 50 Mn 37 Sn 13 and studied its microstr...

Highly hexagonally ordered CoPd alloy nanowire arrays were synthesized through electrochemical deposition techniques into the nanopores of anodic alumina membranes used as templates. Two different electrolytes were used for this purpose, one with pH = 4.1 and the other with pH = 7. Under applying different electrodeposition parameters and by adjusting both, the current density and the electrolyte composition, it could be possible make to vary the composition of CoPd alloy nanowires in a wide range. Their composition and morphology were investigated by SEM and EDX. The magnetic properties of the nanowires array have been measured with a VSM as a function of the temperature, ranging from RT down to 50 K, for different CoPd alloy nanowires composition. Also, the temperature influence on the reversible-irreversible magnetization processes related with the magnetization reversal of the CoPd nanowires array has been analyzed by first order reversal curve (FORC) method.

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In the annealed samples the magnetization changes associated to the magnetic and structural transitions are more abrupt and magnetization isotherms in both the austenitic and martensitic existence region show higher initial magnetic susceptibility and faster approach to saturation. Field-cooled hysteresis loops at 10 K were shifted along the negative H-axis for both samples, but a significant anomaly was evident on the left side of the hysteresis loop for as-quenched ribbons.