Structural, microstructural and magnetocaloric investigations in high-energy ball milled Ni2.18Mn0.82Ga powders

摘要

In this paper, structural, microstrucutural and magnetocaloric properties of Ni2.18Mn0.82Ga alloys submitted to high-energy ball milling are reported. A 7-layered orthorhombic martensitic (Pnnm) phase was detected in post-milling annealed samples, which reached a microstrucuture composed predominantly by nanograins. The magnetocaloric effect is strongly weakened in comparison with ascast samples of similar composition. This effect can be attributed to the absence of the mesoscale twin-related martensitic variants in the nanostructurated powders. However, post-milled samples annealed at 1123 K for 4 h present relative cooling powers as high as those observed for manganites. Therefore, these materials can be considered as potential candidates for use as regenerators in prototypal magnetic refrigerators.