Effect of annealing on the structure and magnetic entropy change of Mn1.1Fe0.9P0.8Ge0.2 ribbons

In this study, we report the effect of annealing temperature on the phase constitution, microstructure and magnetocaloric properties of Mn1.1Fe0.9P0.8Ge0.2 melt-spun ribbons. The secondary phases were formed upon annealing at 1073 and 1173 K, whereas the pure Fe2P-typed phase was formed after a higher temperature annealing at 1273 K. A huge thermal hysteresis of about 40 K width was observed in the first magnetostructural transition cycle. However, during the second cycle it was drastically reduced down almost to zero. A large magnetic entropy change ΔS for ribbons annealed 1273 K is estimated to be 23 J/kg K for a field change of 5 T.