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
\(T_{C}\)
, magnetic and magnetocaloric properties of Mn
_1.05
Ni
_0.85−x
Co
_x
Ge (
\(x = 0\)
–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
_1.05
Ni
_0.85−x
Co
_x
Ge
\((x=0\)
–0.85) ribbons crystallize in hexagonal Ni
₂
In-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 (
\(-\Delta S_{M}\)
) 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.