Enhanced Field Induced Martensitic Phase Transition and Magnetocaloric Effect in Ni₅₅Mn₂₀Ga₂₅ Metallic Foams

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_54.8Mn _20.2Ga_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 and a 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.