Magnetic properties and large magnetic-field-induced strains in off-stoichiometric Ni-Mn-Al Heusler alloys

Magnetic properties and magnetic-field-induced strains (MFIS) have been investigated for off-stoichiometric Ni-Mn-Al Heusler alloys with an ordered L2(1) structure. A clear martensitic transformation in Ni53Mn25Al22 alloy was revealed below the Curie temperature. In the polycrystalline specimen, an irreversible relative change due to the MFIS was confirmed between the martensite start and finish temperatures M-s and M-f, and a maximum relative length change DeltaL/L\(7T) of about -100 ppm was observed at just above M-f. On the other hand, a large irreversible relative length change of about 1000 ppm has been demonstrated in the magnetic field of 7 T for a single crystal cut from the polycrystalline specimen. A delay of the response of strains against the magnetic field was also confirmed. (C) 2000 American Institute of Physics. [S0003-6951(00)01645-4].