STRUCTURAL AND MARTENSITIC TRANSFORMATION OF BULK, DISORDERED AND NANOCRYSTALLINE Ni2MnGa ALLOYS

Abstract

Ferromagnetic Ni2MnGa nanoparticles were prepared by post milling and annealing method. Differential scanning calorimetry studies confirm absence of martensitic and Curie transformation in the disordered state. It was found that the bulk alloy was annealed into a well-defined 7 M structure at around 1073 K. The residual stress of nanoparticles induced the disordered phase to transform into a NM tetragonal phase through atomic ordering. Thermo hysteresis curve of the 'disordered' powder was linear and revealed very low moment indicative of paramagnetic nature. It is confirmed that the martensitic transformation in nanosized particles is predominantly dependent on the strain and the particles size.