Large spontaneous shape memory and magnetic-field induced strain in Ni51Mn25.5Ga23.5 single crystal

Martensitic transformations and characteristics of the magnetic‐field‐induced strain (MFIS) on a nearly stoichiometric Ni51Mn25.5Ga23.5 single crystal have systematically been investigated by various methods, such as ac magnetic susceptibility, resistance, strain measurements and metallographic observations. A large spontaneous strain of 1.62% corresponding to a two‐way thermoelastic shape memory effect is obtained in the single crystal, which is attributed to the high level of oriented internal stress and the preferential orientation of the martensitic variants. When the sample is cooled in a dc magnetic field applied perpendicular to the measuring direction of strain, a large and reversible MFIS up to 1.5% is found. This value of 1.5% is approximately two times larger than that detected in zero field cooling. The results are discussed with respect to growth mechanism of single crystals and the shape memory characteristics. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)