Magnetic and magnetocaloric properties of the alloys Mn2−xFexP0.5As0.5 (0⩽x⩽0.5)

Abstract

The results of investigations of the magnetic and magnetocaloric properties of alloys from the system Mn2−xFexP0.5As0.5 (0⩽x⩽0.5) are presented. The magnetization measurements are performed in the temperature interval 4.2–700K in magnetic fields up to 8T. The entropy changes ΔS with the magnetic field changing from 0 to 2, 4, 5, and 8T are determined from the magnetization isotherms obtained near temperatures of the spontaneous appearance of the ferromagnetic state (TC,TAF–FM1), and the curves ΔS(T0) are constructed. It is found that TC and TAF–FM1 decrease monotonically with increasing manganese concentration and that the ferromagnetic phase is completely suppressed in Mn1.5Fe0.5P0.5As0.5. It is found that the concentration dependences of the maximum entropy jump (and the corresponding cold-storage capacity) and the magnitudes of the ferromagnetic moment of the unit cell with maxima for x=0.9 and 0.8 show extremal behavior. The data obtained are compared with the ferromagnetic moments calculated from first principles by the Korringa-Kohn-Rostoker method using the coherent-potential approximation (KKR-CPA)—the discrepancy for 0.5⩽x⩽0.7 is attributed to the appearance of an antiferromagnetic component of the magnetic structure. It is concluded that the alloys Mn2−xFexP0.5As0.5 have promise for use in magnetic refrigerators operating at room temperature.