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13 August 2003 Shape memory effect and magnetostriction of sputtered NiMnGa thin films
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NiMnGa thin films have been deposited by magnetron sputtering on Mo substrates using a Ni50Mn30Ga20 powder metallurgical target. Independent from variation of substrate temperature during the sputtering process the deposited films are found to be polycrystalline. X-ray diffraction patterns show a decreasing peak width and a shift to slightly higher Bragg angles with increasing substrate temperature during sputtering, which is even amplified when subsequent rapid thermal annealing is applied. Annealing temperatures above 500°C lead to a remarkable enhancement of the shape memory effect as well as of the magnetostriction. Temperature induced martensitic transformations have been measured by a cantilever deflection technique and a cantilever resonance method. Martensitic start temperatures (MS) range between 50 and 90°C depending on composition and annealing temperature. Stress relief upon the martensitic transformation ranges between 200 and 300 MPa whereas the magnetostrictive coupling constant b is about 2 MPa. Magnetization measurements and Curie temperature determination reveal ferromagnetic behavior within the temperature range of the martensitic transformation.
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Holger Rumpf, Juergen Feydt, Daniel Lewandowski, Alfred Ludwig, Bernhard Winzek, Eckhard Quandt, Peng Zhao, and Manfred R. Wuttig "Shape memory effect and magnetostriction of sputtered NiMnGa thin films", Proc. SPIE 5053, Smart Structures and Materials 2003: Active Materials: Behavior and Mechanics, (13 August 2003);

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