Giant magnetocaloric effect in Co2FeAl Heusler alloy nanoparticles.

A giant magnetocaloric effect across the ferromagnetic to paramagnetic phase transition was observed in chemically synthesized Co2FeAl Heusler nanoparticles with a mean diameter of around 16 nm. In our previous report, we have observed a significant enhancement in its saturation magnetization (Ms) and Curie temperature (Tc) as compared with its bulk counterpart. Motivated from those results, here, we aim to explore its magnetocaloric properties near Tc. The magnetic entropy change shows a positive anomaly at 1252 K. The magnetic entropy change increases linearly with the magnetic field, and a large value of 15 J/Kg is detected under a moderate field of 14 k Oe across the Tc. It leads to a net relative cooling power of 89 J/Kg for the magnetic field change of 14 k Oe. To confirm the nature of the magnetic phase transition, a detailed study of its magnetization was performed. The Arrott plot and the nature of the universal curve concludes that the ferromagnetic to paramagnetic phase transition in the present system is of second order. The possibility of using Co2FeAl alloy in multistage magnetic refrigeration is also discussed.