The overlap of first- and second-order phase transitions and related magnetic entropy changes in [Ni.sub.2+x][Mn.sub.1-x] Ga Heusler alloys

A study of the magnetostructural phase transition and related magnetic entropy changes, [DELTA] [S.sub.M], in the vicinity of a first-order magnetostructural transition, in polycrystalline shape memory alloys [Ni.sub.2+x][Mn.sub.1-x] Ga (x = 0.16, 0.17, 0.18, 0.19, 0.20) have been done. Thermal expansion measurements reveal the gradual overlap of the first- and second-order phase transitions that results in the large magnetic entropy changes in the alloys. We observed a magnetic entropy change of [DELTA] [S.sub.M] = -66.2 J/[kg.sup.-1] * [K.sup.-1] between 350 K and 350.5 K in a field change of 5 T in [Ni.sub.2+x][Mn.sub.1-x] Ga for x = 0.19. Index Terms--Magnetic materials, magnetoelasticity.