The effect of partial substitution of in by Si on the phase transitions and respective magnetic entropy changes of Ni₅₀Mn₃₅In ₁₅ Heusler alloy

The effect of the partial substitution of In by Si on the crystal structure, phase transition temperatures and respective magnetic entropy changes in Ni₅₀Mn₃₅In_15-xSi_x with 1 ≤ x ≤ 5 have been determined using room temperature x-ray diffraction and magnetization measurements in the temperature interval 5-400 K and in magnetic fields up to 5 T. The results show that small amount of Si in the In position results a significant influence in the inverse magnetocaloric effect accompanied with the martensitic transitions in these compounds. The peak values of positive magnetic entropy change for magnetic field changes H = 5 T is found to depend on composition and vary from 82 J Kg^-1 K^-1 for x = 1 (at T = 275 K) to 124 J Kg^-1 K^-1 for x = 3 (at T = 239 K). It is found that the substitution of 20% In atoms by Si in Ni ₅₀Mn₃₅In₁₅ results in an increase in positive magnetic entropy changes of more than 300%. This system also shows a negative entropy change at the Curie temperature, making this a candidate material for application in a refrigeration cycle that exploits both positive and negative magnetic entropy changes.