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

Abstract

Magnetic properties and magnetic-field-induced strains (MFIS) have been investigated for off-stoichiometric Ni–Mn–Al Heusler alloys with an ordered ${\text{L2}}_1$ structure. A clear martensitic transformation in ${\mathrm{Ni}}_{\mathrm{53}}{\mathrm{Mn}}_{\mathrm{25}}{\mathrm{Al}}_{\mathrm{22}}$ 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 ${\mathrm{\Delta L/L|}}_{7\mathrm{T}}$ 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.