Study of Co-containing Ni-Mn-Ga by positron annihilation

Positron annihilation spectroscopy measurements have been carried out in the ferromagnetic shape memory alloy Ni-Mn-Ga-Co. Positron experiments have been performed at room temperature after subsequent isochronal annealing up to 600 °C. Positron lifetime results have been compared with Differential Scanning Analysis experiments performed in the same samples. Experiments show a large variation of the average positron lifetime values with the annealing temperature of the samples, indicating a clear relation between the concentration of vacancies and the properties of the martensitic transformations of these alloys.