Study of austenite-martensite transformation in Ni-Mn-Ga magnetic shape memory alloy

L. Straka; O. Heczko; V. Novák; N. Lanska

doi:doi:10.1051/jp4:20031029

Issue		J. Phys. IV France Volume 112, October 2003


Page(s)		911 - 915
DOI		https://doi.org/10.1051/jp4:20031029

J. Phys. IV France 112 (2003) 911
DOI: 10.1051/jp4:20031029

Study of austenite-martensite transformation in Ni-Mn-Ga magnetic shape memory alloy

L. 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

Abstract
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 ${\rm T_A} = 317$ K, ${\rm T_M} = 308$ K were determined by AC susceptibility measurement. Structure parameters obtained from X-ray measurement are ${\rm a_A} = 0.584$ nm for austenite and ${\rm a_M} = {\rm b_M} = 0.595$ nm, ${\rm c_M} = 0.561$ 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.