New Sequences of Phase Transition in Ni-Mn-Ga Ferromagnetic Shape Memory Nanoparticles

In-situ high-energy X-ray diffraction was used for tracing the structural transitions in Ni2MnGa and Ni47Mn25Ga22Co6 nanoparticles that were prepared by a ball-milling and subsequent annealing process. A decrease in martensitic transformation temperature was evidenced in all annealed nanoparticles. It was found that a three-layered modulated structure, usually observed as a metastable premartensitic phase in coarse-grained alloys, becomes a stable phase in the annealed Ni2MnGa nanoparticles up to 4 K.