Comparison of magnetocaloric properties of the Mn2-xFexP0.5As0.5 (x = 1.0 and 0.7) compounds

The Mn_2-xFe_xP_0.5As_0.5 compounds (x = 0.7 and 1.0) studied exhibit the magnetic phase transitions, which are accompanied by a magnetic entropy change. For x = 1 the PM-FM transition is of the first order one with a weak (2-3 K) thermal hysteresis in the vicinity of T_C = 275 K. The Mn_1.3Fe_0.7P_0.5As_0.5 compound possesses two magnetic transitions: the second-order PM-FM transition at T_C = 190 K, followed by the FM-AFM transition at T_N = 90 K, leading to normal and inverse magnetocaloric effects, respectively. The maximum values of magnetic entropy change are equal to 17 J kg^-1 K^-1 in MnFeP_0.5As_0.5 and 5 J kg^-1 K^-1 in Mn_1.3Fe_0.7P_0.5As_0.5 for a field change of 5 T. The magnetic entropy changes were calculated using both the isofield magnetization curves versus temperature and the isothermal magnetization curves versus applied magnetic field. The magnetocaloric effect in MnFeAs_0.5P_0.5 is discussed in the terms of both the thermodynamic Maxwell relation and the Clausius-Clapeyron equation.