Structural, microstructural and magnetocaloric investigations in high-energy ball milled powders

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 as-cast 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.