Recent Breakthrough Development of the MSM Effect in Ni-Mn-Ga Alloys

O. Söderberg¹ , Y. Ge¹, A. Sozinov², S.–P. Hannula¹ and V. K. Lindroos¹

¹Laboratory of Physical Metallurgy and Materials Science, Helsinki University of Technology, P.O. Box 6200, Fin-02015 HUT, Finland

²Laboratory of Biomedical Engineering, Helsinki University of Technology, P.O. Box 2200, FIN-02015 HUT, Finland

Magnetic Shape Memory (MSM) alloys or Ferromagnetic Shape Memory Alloy (FSMA) materials discovered by Ullakko et al. [1] are attained increasing interest due to their ability to produce a large strain with rather high frequencies without a change in the external temperature. These materials are shown to have potential for actuator and sensor applications [2].  MSM materials exhibit giant magnetic field-induced strain (MFIS) based on the rearrangements of the crystallographic domains (twin variants). The magnetization energy of the material is lowered when such twin variants, that have the easy axis of magnetization along the field, start to grow due to twin boundary motion. Currently, the best working MSM materials are the near stoichiometric, highly composition dependent Ni₂MnGa Heusler alloys, in which the modulated martensitic structures (referred according to the modulation 5M and 7M) has given 6 % or 10 % response in a magnetic field less than 800 kA/m [3-6]. One of the main issues in application of MSM effect is the working temperature range that is at present shown to be between 150-333 K [7]. The optimal frequency region for 5M Ni-Mn-Ga MSM alloys is given in ref. [8] to be below 500 Hz. The fatigue life of such MSM elements has been shown to be at least 50 x 10⁶ shape change cycles [2]. In the present lecture, the research work carried out at Helsinki University of Technology in MSM group during years 1998-2003 will be presented.

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4. Sozinov A, Likhachev A A, Lanska N, Söderberg O, Ullakko K and Lindroos V K 2003 Effect of crystal structure on magnetic-field-induced strain in Ni-Mn-Ga. Proc. SPIE 5053 (2003) 586-594.

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7. Heczko O and Straka L, Temperature dependence and temperature limits of magnetic shape memory effect.  J. Appl. Phys. 94 (2003) 7139-7143.

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