Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni Mn Ga Heusler alloy

We have studied the isothermal entropy change around a first-order structural transformation and in correspondence to the second-order Curie transition in the ferromagnetic Heusler alloy Ni_2.15Mn_0.85Ga. The results have been compared with those obtained for the composition Ni_2.19Mn_0.81Ga, in which the martensitic structural transformation and the magnetic transition occur simultaneously. With a magnetic field span from 0 to 1.6 T, the magnetic entropy change reaches the value of 20 J/kg K when transitions are co-occurring, while 5 J/kg K is found when the only structural transition occurs. Received 27 September 2002 / Received in final form 17 February 2003 Published online 11 April 2003 RID="a" ID="a"e-mail: solzi@fis.unipr.it