Martensitic structure and magnetic domain transformation in melt-spun Ni-Mn-Ga ferromagnetic ribbons

摘要

Ni_(53)Mn_(23.8)Ga_(23.2) ribbons were fabricated by melt-spinning and subsequent high vacuum annealing process. The structure and magnetic properties of the as-spun and annealed ribbons were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and vibrating sample magnetometer. All the samples exhibit an orthorhornbic structure of a seven-layered modulation at room temperature. The martensitic and its reverse transformation were clearly observed on all the samples. With increasing annealing temperature, the saturation magnetization increases while the coercivity decreases. It was found that the transformation becomes drastic in the sample annealed at 1073 K. In addition, an in situ observation on the evolution of magnetic domain patterns with temperature was carried out by means of magnetic force microscopy (MEM).