Ni-Mn-Ga ferromagnetic shape memory wires

Ni-Mn-Ga ferromagnetic shape memory wires (Ni2.10Mn0.98Ga0.92, mean diameter 170 mu m) are obtained by the rotating water bath melt spinning technique. The compositional heterogeneity linked to its dendritelike structure gives rise to a complex and broad martensitic transformation (MT). The reduced value of magnetization in the as-spun sample is ascribed to Mn-Mn antiferromagnetic interactions at structural defects as atomic disorder, vacancies, and antiphase boundaries structures. Moreover, the observed low temperature magnetic relaxation process is characterized by a splitting in the zero-field-cooled/field-cooled magnetization curves and the frequency shift in the ac magnetic susceptibility. The results are interpreted in terms of the coexistence of a reduced magnetization state and nearly noninteracting magnetic clusters. A high temperature treatment optimizes both the MT and the magnetic characteristics (i.e., decrease in the hysteresis of the MT and magnetization recovery, respectively). (C) 2010 American Institute of Physics. [doi:10.1063/1.3445265]