Phase transitions and magnetocaloric effects in the Heusler compounds Ni₂Mn_0.70Cu_0.30Ga and Ni₂Mn_0.70Cu_0.25Cr_0.05Ga

The structural, magnetic and magnetocaloric properties of Ni₂Mn_0.70Cu_0.25Cr_0.05Ga and Ni₂Mn_0.70Cu_0.30Ga Heusler alloys have been investigated by x-ray diffraction, magnetization, transport, and DSC measurements. For the Ni₂Mn_0.70Cu_0.25Cr_0.05Ga alloy, a first order coupled magnetostructural phase transformation near room temperature with a thermal hysteresis of <!--[endif]---->1 K was observed. In the vicinity of the transition, large magnetic entropy changes of ~39 J/kg K (while (warming) and ~17 J/kg K (while cooling) was observed for a field change of 50 kOe. For the Ni₂Mn_0.70Cu_0.30Ga material, the first order phase transition with a thermal hysteresis of ~7 K was observed near 345 K. For a field change of 50 kOe, peak magnetic entropy changes of -17 J/kg K and -33 J/kg K were observed for warming and cooling, respectively. The electrical resistivity data showed interesting behavior near the phase transitions. The experimental results will be presented and discussed considering the coupling and de-coupling of the first order structural and second order magnetic phase transitions in the materials.<!--![endif]---->