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

摘要

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 ${rm Ni}_{2}{rm MnGa}$ in an attempt to make the magnetic and structural transition temperatures, ${rm T}_{rm C}$ and ${rm T}_{rm M}$, 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 ${rm T}_{rm M}$ and decreased ${rm T}_{rm C}$, 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).