J. Phys. IV France 11 (2001) Pr8-287-Pr8-292
The behaviour of Ni-Mn-Ga martensitic alloys in magnetic fieldO. Söderberg1, Y. Ge1, N. Glavatska2, O. Heczko3, K. Ullakko3 and V.K. Lindroos1
1 Helsinki University of Technology, Laboratory of Physical Metallurgy and Materials Science, P.O. Box 6200, 02015 Hut, Finland
2 Institute for Meta1 Physics, Department of Alloyed Steels, 003680 Kiev 142, Ukraine
3 Helsinki University of Technology, Laboratory of Biomedical Engineering, P.O. Box 2200, 02015 Hut, Finland
Some of the Ni-Mn-Ga alloys exhibit a large shape change in magnetic field. This phenomenon occurs in their martensitic state and it is called the magnetic shape memory (MSM), since these materials can change their dimensions when the direction of the magnetic field varies. This kind of behaviour can be utilised in actuators and sensors. In the present work, three different polycrystalline Ni-Mn-Ga alloys are studied. The transformation temperatures together with the ferromagnetic Curie temperatures are determined by the magnetic susceptibility measurement and confirmed by the optical differential scanning calorimetry. The structures of the alloys are investigated with the optical microscopy and the X-ray θ-2θ-method. The sample behaviour in magnetic field is studied both by the vibrating sample magnetometer and by measuring magnetic-field-induced strain. Also, the effect of thermal, static and dynamic magneto-thermal cycling on the behaviour of the alloys in magnetic field is studied.
© EDP Sciences 2001