First-order magnetic and magnetostructural transitions in the magnetocaloric compound MnNi0.73Fe0.27Ge

Magnetic and magnetostructural transitions of MnNi0.73Fe0.27Ge have been studied by calorimetry and by magnetic measurements. The first-order MST from paramagnetic to ferromagnetic martensite shows a giant magnetic entropy change of −27 J/kg K for a magnetic-field change of 50 kOe around 233 K. A weak first-order magnetic transition is observed in the martensite phase over a large low-temperature range, with clear thermal hysteresis and increased saturation field. The origin is discussed on the basis of the competitiom between ferromagnetic and antiferromagnetic coupling with magneto-elastic coupling.