The effect of partial substitution of In by Si on the phase transitions and respective magnetic entropy changes of Ni50Mn35In15 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 Ni(50)Mn(35)In(15-x) Si(x) with 1 <= x <= 5 have been determined using room temperature x- ray diffraction and magnetization measurements in the temperature interval 5 - 400K 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 JKg(-1) K(-1) for x = 1 (at T = 275 K) to 124JKg(-1) K(-1) for x = 3 (at T = 239 K). It is found that the substitution of 20% In atoms by Si in Ni(50)Mn(35)In(15) 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.