Enhanced magnetocaloric performances and tunable martensitic transformation in Ni35Co15Mn35−xFexTi15 all-d-metal Heusler alloys by chemical and physical pressures

Abstract

The solid-state magnetic cooling (MC) method based on the magnetocaloric effect (MCE) is recognized as an environmentally friendly and high-energy-efficiency technology. The search or design of suitable magnetic materials with large MCEs is one of the main targets at present. In this work, we apply the chemical and hydrostatic pressures in the Ni35Co15Mn35−xFexTi15 all-d-metal Heusler alloys and systematically investigate their crystal structures, phases, and magnetocaloric performances experimentally and theoretically. All the alloys are found to crystallize in an ordered B2-type structure at room temperature and the atoms of Fe are confirmed to all occupy at sites Mn(B). The total magnetic moments decrease gradually with increasing Fe content and decreasing of volume as well. The martensitic transformation temperature decreases with the increase of Fe content, whereas increases with increasing hydrostatic pressure. Moreover, obviously enhanced magnetocaloric performances can also be obtained by applied pressures. The maximum values of magnetic entropy change and refrigeration capacity are as high as 15.61(24.20) J (kg K)−1 and 109.91(347.26) J kg−1 with ΔH = 20(50) kOe, respectively. These magnetocaloric performances are superior to most of the recently reported famous materials, indicating the potential application for active MC.