Magnetic Phase Transition and Magnetocaloric Effect in Co-Doped Mn-Ni-Ge Melt-Spun Ribbons

The effects of Co substitution for Ni on Curie temperature TC, magnetic and magnetocaloric properties of Mn_1.05Ni_0.85-x Co_xGe (x = 0-0.85) alloy ribbons prepared by melt-spinning have been investigated by means of X-ray diffraction and magnetization measurements. All the as-spun Mn_1.05Ni_0.85-xCo_xGe (x = 0-0.85) ribbons crystallize in hexagonal Ni₂In-type structure at room temperature. The magnetic measurements at 100 K show that the as-spun ribbons exhibit good soft-magnetic behaviors with coercivity <;100 Oe. No martensitic magnetostructural transition can be observed in magnetization versus temperature M-T curves, whereas the Curie temperature T_C of the ferromagnetic to paramagnetic transitions of these ribbons increases from 205 K for x = 0 to 295 K for x = 0.85. The peak values of the maximal magnetic entropy changes (-ΔS_M) decrease from 6.0 to 3.4 J/kg K around T_C, under a field change of 0-50 kOe as x increases from 0 to 0.85, while the value of refrigeration capacity varies in the range of 170-250 J/kg.