Martensitic Transitions and Magnetocaloric Properties in ${\hbox {Ni}}_{48}{\hbox {Mn}}_{39}{\hbox {In}}_{13\hbox {-}{\rm x}}{\hbox {Ge}}_{\rm x} ({\rm x} = 1\hbox {-}3)$

The effects of partial Ge substitution for In on phase transformation and magnetocaloric properties in annealed Ni₄₈Mn₃₉In_13-xGe_x (x = 1-3) ribbons were studied using X-ray diffraction and magnetization measurements. The ribbons for x ≤ 2 crystallize in a cubic L21 ordered phase structure, while Ni₄₈Mn₃₉In₁₀Ge₃ ribbon is in the martensitic phase with a modulated structure at room temperature. The martensitic structural transition temperature (T_M) increases from 220 K for x = 1 to 320 K for x = 3 with increasing Ge content. The positive magnetic entropy changes (ΔS_M), 29.6, 28.0 J/kg K for x = 1, 2, respectively, were found for a magnetic field change H = 50 kOe. The hysteresis loss and net refrigeration capacity ( RC) were also observed to change significantly. The largest value of the net RC (330 J/kg) for the second order phase transition was found for x = 1 at T_C = 280 K, with negative ΔS_M = -6.5 J/kg k at ΔH=50 kOe. These values are comparable to those of rare earth based systems near room temperature.