Enhanced field induced martensitic phase transition and magnetocaloric effect in Ni_(55)Mn_(20)Ga_(25) metallic foams

摘要

The high surface/volume ratio and mechanical stability under cyclic strain makes polycrystalline Ni—Mn-Ga metallic foams attractive for magnetic refrigeration. By means of comparison with a polycrystalline bulk material, we have demonstrated that the porous structure of Ni_(54.8)Mn_(20.2)Ga_(25.0) open-cells metallic foams (porosity varying between 44% and 58%) reduces the temperature span of the phase transition and increases the magnetocaloric effect (MCE). MCE was investigated using calorimetry in a magnetic field. Temperature scan and isothermal experiments have shown a 0.8 K T~(-1) shift of the phase transition temperature anda maximum irreversible entropy change of 2.5 Jkg~(-1) K~(-1) . The results indicate that metallic foams can represent a good approach for enhancing field induced phase transitions in magnetic refrigeration applications.