Magnetostriction in ferromagnetic shape memory alloys

There is intense interest in the development of new magnetostrictive materi als having large strains. Recent experiments [1,2] showed that the ferromag netic shape memory alloys (SMA) have some perspectives to generate signific ant magnetic-fleld-induced deformations. Taking into account the high mobil ity of the martensite crystal lattice variants, the corresponding magnetic measurements were performed by using the SMA Ni-Mn-Ga and Fe-Pd. It is conc luded 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 star t temperature). Magnetic property anomalies accompany this phase transition which can be interpreted as a transition to an intermediate phase. The cha racteristic temperatures M-s and T-i are close in some alloys. The simultan eous action of the lattice instabilities connected with the formation of ma rtensite and intermediate phases produces the essential decreasing of the e lastic constants and as a result the strong growth of the high temperature phase magnetostriction nearly at T = M-s. The behavior of the martensitic p hases in magnetic field is also discussed. (C) 2001 Published by Elsevier S cience B.V.