J. Phys. IV France 112 (2003) 911
Study of austenite-martensite transformation in Ni-Mn-Ga magnetic shape memory alloyL. Straka1, O. Heczko1, V. Novák2 and N. Lanska1
1 Laboratory of Biomedical Engineering, Department of Engineering Physics and Mathematics, Helsinki University of Technology, P. O. Box 2200, Espoo, Finland
2 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 18221 Prague 8, Czech Republic
Ni 49.7Mn 29.1 Ga 21.2 magnetic shape memory sample showing magnetic-field-induced strain of 5.7 % in the magnetic field 0.5 T was studied at different conditions during austenite-martensite and martensite-austenite transformations. Transformation temperatures K, K were determined by AC susceptibility measurement. Structure parameters obtained from X-ray measurement are nm for austenite and nm, nm for martensite which has fivelayered modulated structure. Mechanical stress up to 4 MPa and magnetic field up to 1 T were applied in order to study their influence on the transformations. Totally 39 transformation cycles were measured. The thermoelastic strains during transformations vary from -3.6 % to +1.8 %. Simultaneous change of magnetization and strain has been observed. Thermomechanical and magnetic history of the sample seems to have no or only very weak influence on the character of austenite-martensite transformation and no clear trend emerges in our experiments.
© EDP Sciences 2003