Martensitic transformation and shape memory effect of Ni-rich Ni2MnGa sputtered films under magnetic field

Ohtsuka, Makoto; Matsumoto, M.; Koike, K.; Takagi, Toshiyuki; Itagaki, Kimio

doi:10.1016/j.jmmm.2006.10.1048

Cited by 7 publications

(3 citation statements)

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“…Interestingly, the largest MFIS was obtained for the thinnest (0.1 μm) of all films on Mo. Ohtsuka et al116 found an MFIS of close to 0.04% for 5 μm thick Ni‐Mn‐Ga films on 14 μm polyvinyl alcohol (PVA) substrates. Due to the bimaterial effect, large deflections can be obtained in bilayers as a result of magnetic‐field‐induced and thermally induced martensitic transformations.…”

Section: Structural Elements With One or More Small Dimensionsmentioning

confidence: 99%

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Size Effects on Magnetic Actuation in Ni‐Mn‐Ga Shape‐Memory Alloys

2010

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The off-stoichiometric Ni(2)MnGa Heusler alloy is a magnetic shape-memory alloy capable of reversible magnetic-field-induced strains (MFIS). These are generated by twin boundaries moving under the influence of an internal stress produced by a magnetic field through the magnetocrystalline anisotropy. While MFIS are very large (up to 10%) for monocrystalline Ni-Mn-Ga, they are near zero (<0.01%) in fine-grained polycrystals due to incompatibilities during twinning of neighboring grains and the resulting internal geometrical constraints. By growing the grains and/or shrinking the sample, the grain size becomes comparable to one or more characteristic sample sizes (film thickness, wire or strut diameter, ribbon width, particle diameter, etc), and the grains become surrounded by free space. This reduces the incompatibilities between neighboring grains and can favor twinning and thus increase the MFIS. This approach was validated recently with very large MFIS (0.2-8%) measured in Ni-Mn-Ga fibers and foams with bamboo grains with dimensions similar to the fiber or strut diameters and in thin plates where grain diameters are comparable to plate thickness. Here, we review processing, micro- and macrostructure, and magneto-mechanical properties of (i) Ni-Mn-Ga powders, fibers, ribbons and films with one or more small dimension, which are amenable to the growth of bamboo grains leading to large MFIS, and (ii) "constructs" from these structural elements (e.g., mats, laminates, textiles, foams and composites). Various strategies are proposed to accentuate this geometric effect which enables large MFIS in polycrystalline Ni-Mn-Ga by matching grain and sample sizes.

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Section: Structural Elements With One or More Small Dimensionsmentioning

confidence: 99%

“…Polymer substrates include polyvinyl alcohol (PVA)116 and photoresist 151. The large compliance of these substrates allows for deposition of rather thick Ni‐Mn‐Ga films: Kohl et al 117 grew 10 μm thick films on PVA.…”

Section: Three‐dimensional Aggregates and Constructsmentioning

confidence: 99%

Size Effects on Magnetic Actuation in Ni‐Mn‐Ga Shape‐Memory Alloys

2010

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“…Therefore, the studies concerning solidification, crystal growth and diffusion -such as [82,83] for Ni-Mn-Ga alloys, [84] for Co-Ni-Ga alloys, [85] for Ni-Co-Mn-In alloys, [86] for Ni-Mn-Sn alloys -as well as annealing and ordering of the material [87][88][89][90][91] are valuable. In addition to the bulk sample fabrication, there has been great interest especially to develop the fabrication of the thin films [for example [92][93][94][95][96][97][98][99][100][101][102][103][104], since this has turned out to be quite challenging. Only during the recent year the applied substrate materials have varied from silicon [92,102,103].…”

Section: Fabricationmentioning

confidence: 99%

Recent Developments of Magnetic SMA

Söderberg¹,

Aaltio

et al. 2008

Advances in Science and Technology

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In the shape memory alloys (SMAs) the thermal triggering induces reversible dimensional change by the phase transformation – these materials may also be ferrior ferromagnetic, however, here only the ferromagnetic SMAs are discussed. In certain SMAs the austenitemartensite phase transformation is influenced by the magnetic field as either austenite or martensite is promoted by the field and this is exploited for the dimensional changes. However, in the magnetic shape memory (MSM) alloys no phase transformation occurs as the remarkable dimensional changes take place by the twin variant changes in the martensitic phase activated by the external magnetic field at constant temperature. In addition to the phase transformation or magnetic shape memory effect, the applied magnetic field may also result in the conventional magnetostriction (MS), enhance the superelasticity (magneticfieldassisted superelasticity MFAS) or induce the giant magnetocaloric effect (GMCE). Certain alloys such as NiMnGa may even be multifunctional showing more than one of these effects. The present paper gives an overview of the different types of the magnetically activated SMA alloys, their properties as well as their potentials for applications in the frameworks of the recent studies.

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