The Overlap of First- and Second-Order Phase Transitions and Related Magnetic Entropy Changes in Ni$_2 + x$Mn$_1 - x$Ga Heusler Alloys

A study of the magnetostructural phase transition and related magnetic entropy changes, DeltaS
_M
, in the vicinity of a first-order magnetostructural transition, in polycrystalline shape memory alloys Ni
_2+x
Mn
_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 DeltaS
_M
=-66.2 J/kg
^-1
middotK
^-1
between 350 K and 350.5 K in a field change of 5 T in Ni
_2+x
Mn
_1-x
Ga for x=0.19