Magnetostriction in ferromagnetic shape memory alloys

There is intense interest in the development of new magnetostrictive materials having large strains. Recent experiments [1,2] showed that the ferromagnetic shape memory alloys (SMA) have some perspectives to generate significant magnetic-fleld-induced deformations. Taking into account the high mobility of the martensite crystal lattice variants, the corresponding magnetic measurements were performed by using the SMA Ni-Mn-Ga and Fe-Pd. It is concluded that the condensation of the soft acoustic phonon mode TA2 (q = 1/3 < 110 >) takes place at T = T-i > M-s in Ni-Mn-Ga alloy (M-s-martensite start temperature). Magnetic property anomalies accompany this phase transition which can be interpreted as a transition to an intermediate phase. The characteristic temperatures M-s and T-i are close in some alloys. The simultaneous action of the lattice instabilities connected with the formation of martensite and intermediate phases produces the essential decreasing of the elastic constants and as a result the strong growth of the high temperature phase magnetostriction nearly at T = M-s. The behavior of the martensitic phases in magnetic field is also discussed. (C) 2001 Published by Elsevier Science B.V.