Influence of the Magnetic Anisotropy on the Magnetic Entropy Change of ${\rm Ni}_{2}{\rm Mn}({\rm Ga},{\rm Bi})$ Memory Shape Alloy

The magnetocaloric effect (MCE) is a good chance to create a more efficient refrigeration technique, both in energy and environmental friendliness. On the search for materials with large MCE (mainly characterized by a great magnetic entropy variation) in a wide temperature range around room temperature, this work focuses on the widely studied Heusler alloy and the influence of bismuth alloying in the stoichiometry Ni₂MnGa in an attempt to make the magnetic and structural transition temperatures, T_C and T_M, come closer, and therefore create a large MCE. In addition, we discuss the influence of alloying processes on the magnetic anisotropy. Our results have in fact increased T_M and decreased T_C, but Bi substitution in Ga site (from 0 up to 5%) has been insufficient to merge those two transitions. The maximum magnetic entropy change was found to be 3.8 J/kg.K for the pure sample (without Bi) and 2.2 J/kg.K for sample 4 (maximum Bi concentration).