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Heusler type alloys Ni50Mn25+xGa25-x (x = 2, 3, 4, and 5) based on near stoichiometric Ni2MnGa compositions were directionally solidified using modified Bridgman method. The alloys thus prepared were characterised for their chemical composition, crystal structure, microstructure, phase transformation, magnetic and magneto-mechanical properties. The directionally solidified Ni50Mn30Ga20 alloy rod exhibited maximum magnetocrystalline value of 95 kJm-3 and lowest detwinning stresses for martensite phase of about 5 MPa. The reversible room temperature magnetic field induced strain of 0.2 per cent under external magnetic field of 0.6 T and 0.05 kN bias load was obtained for the directionally solidified Ni50Mn30Ga20 alloy. [ABSTRACT FROM AUTHOR]

Ferromagnetic shape memory Ni50Mn30Ga15Al5-xBx (x = 0, 1, and 4) alloys were prepared by vacuum arc melting and subsequent heat-treatment as well as by melt spinning to investigate the effect of trivalent element additions in ternary Ni-Mn-Ga alloys. The heat-treated alloys containing Al were reported to possess a modulated martensite structure, however alloy containing both Al and B showed a loss of modulated structure in martensite formed. The rapidly solidified alloys on the other hand showed the formation of a similar modulated structure without composition change in alloys containing Al and the alloys containing Al and B. In addition, the former showed a presence of an amorphous phase with latter showing crystalline boron rich phases. The magnetisation of the B containing alloys in both the processing technique was however very low, showing lower magnetic exchange interaction in such alloys. [ABSTRACT FROM AUTHOR]

Quaternary Ni50 Fex Mn30-x Ga20 (x = 2.5, 5, and 15) and Ni45 Fe5 Mn30 Ga20 alloys based on modification of ferromagnetic shape memory alloy ternary Ni50 Mn30 Ga20 composition prepared by vacuum arc melting and subsequent heat-treatment were investigated to understand the effect of varying Fe-content in Ni-Fe-Mn-Ga alloys. With increasing Fe-content, saturation magnetisation and Curie temperature increased, however martensite transformation temperature did not show a systematic variation. The 57Fe Mossbauer spectra showed three distinct sub-spectra depending upon the site occupancy by Fe-atoms. The results are explained with site selection by Fe-atom in parent L21 lattice. [ABSTRACT FROM AUTHOR]

Abstract: We present a process to fabricate freely movable shape memory alloy (SMA) structures by electron-beam lithography (EBL) and sacrificial layer technology starting from free-standing SMA films. Functional films such as SMA and ferromagnetic SMA films may not be structured on the same substrate used for deposition due to process incompatibilities. In addition, EBL and sacrificial layer technologies entail various constraints and requirements on substrate material and properties. These issues can be solved by introducing a substrate inversion technology that includes deposition of sacrificial structures followed by electroplating of a new metal substrate onto the functional film and release of the initial substrate. This process is demonstrated for a SMA film of NiMn-Ga that has been sputter-deposited on a polymer substrate allowing the fabrication of large arrays of mechanically active SMA nanostructures. [ABSTRACT FROM AUTHOR]

Abstract: In search for new ferromagnetic shape memory alloys (FSMA) we have calculated structural energy differences, magnetic exchange interaction constants and mixing energies of quaternary (X1X2)YZ Heusler alloys with X1,X2,Y =Ni,Co,Fe and Z=Ga, Zn using density functional theory. The comparison of the energy profiles of (NiCo)FeZ, (FeNi)CoZ, and (FeCo)NiZ with Z=Ga and Zn as a function of the tetragonal distortion reveals that the energetically preferred ordering type is (NiCo)FeGa and (NiCo)FeZn which shows that Fe prefers to occupy the same cubic sublattice as Ga or Zn what implies that Fe favors Co and Ni as nearest neighbors, respectively. The Curie temperatures of (NiCo)FeGa and (NiCo)FeZn are high of the order of 600K. (NiCo)FeGa, which has the same valence electron concentration (e/a=7.5) as Ni2MnGa and also possesses a high martensitic transformation temperature (>500K), is of interest for future magnetic shape memory devices. [ABSTRACT FROM AUTHOR]

Abstract: Partial substitution of Ni by Co in Mn-rich Ni–Mn–Ga alloys has been found to modify the magnetic ordering of the phases, improving in this way the possibility to obtain large magnetization difference between austenite and martensite, an essential requirement to induce the martensitic transformation by application of a magnetic field. Particularly, alloys undergo, for Co content below , structural transformation between ferromagnetic austenite and paramagnetic martensite, thus leading to enhanced magnetization difference values. The martensitic transformation temperatures as well as the martensite and austenite Curie temperatures depend on composition, but significant changes can be brought about by selected thermal treatments. In this work, the composition is chosen as in order to obtain concurrent martensitic transformation and austenite Curie temperature, and the effect of quench and subsequent ageing on the structural and magnetic transitions is studied. Aside from the monotonic transformation temperatures change, which is mostly attributed to atomic ordering taking place upon post-quench ageing, the results show the effect of the relative position of the structural and magnetic ordering reactions on the transformation entropy change. [ABSTRACT FROM AUTHOR]

Abstract: Ferromagnetic shape memory alloys (MSMA) are well-known smart materials for actuation applications, due to their large shape change in applied magnetic fields. Off-stoichiometric Ni–Mn–Ga single crystals of MSMA exhibit a magnetic-field induced strain of about 10%. In the past decade a lot of effort has been put into understanding and optimizing the properties of Ni-Mn-Ga alloys in terms of the magnetic shape memory effect, starting with the production of single crystals and going all the way to heat treatment and magneto-mechanical training. Here we focus on and present the production and characterization of single crystal Ni–Mn–Ga alloys with off-stoichiometric composition. The molten material was cast into preheated ceramic shells and directionally solidified in a Bridgman-type process. Cylindrical single crystal bars of diameters up to 48 mm and a length of 110 mm were obtained by using suitable grain selectors. Only small misorientations between the single crystal c-axis and the bar axis were found in these bars. The crystals were characterized in terms of composition, segregation, crystal orientation and microstructural features by means of SEM/EDS, EBSD and light microscopy. [ABSTRACT FROM AUTHOR]