Giant Magnetocaloric Response Induced by Tuning the Intrinsic Exchange Field in the Alloys With Random Magnetic Anisotropy Under a Constant Magnetic Field

The use of a limited magnetic field strength to induce a giant magnetocaloric response is desired towards the potential magnetic refrigeration applications. A method to lower the external magnetic field through taking advantage of the exchange field gradient in the alloys with different component ratios and random magnetic anisotropy under a constant magnetic field is conceived, where the conventional thermodynamic Maxwell formula is modified by replacing the external magnetic field by internal exchange field to calculate magnetic entropy change. The Ni46Co3Mn37-x CuxIn14 (x=0, 1, 2, 3, at.%) alloys are fabricated, and with increasing x, the martensitic transformation temperature increases towards room temperature, meanwhile, the ferromagnetism is weakened and the Curie temperature decreases down to room temperature. Under a constant magnetic field of 1.5 T, it is calculated that an exchange field variation of 1 T can induce a giant positive magnetic entropy change of ~14 J kg-1K-1 near the martensitic transformation and a high relative cooling power ~110 J kg-1 near the paramagnetic-to-ferromagnetic phase transition. Other features of this magnetocaloric effect include that it is weakened under stronger magnetic fields and the relative cooling power is independent of magnetic field. The Monte Carlo simulation is also performed to fit the magnetization and magnetic entropy change behaviors near the magnetic phase transition, and the exchange energy in alloys are quantified from 1.438×10-22 to 1.290×10-22 J with the x variation from 0 to 1 through fitting the linear relative cooling power results. This work not only opens a new avenue to develop a household magnetic refrigerant with low external stimuli and high signal-to-noise ratio, but also provides a method to quantify the intrinsic magnetic parameters using magnetocaloric effect.