Comparison of magnetocaloric properties of the Mn_(2-x)Fe_xP_(0.5)As_(0.5) (x = 1.0 and 0.7) compounds

摘要

The Mn_(2-x)Fe_xP_(0.5)As_(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_(1.3)Fe_(0.7)P_(0.5)As_(0.5) compound possesses two magnetic transitions: the second-order PM-FM transition at Tc = 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_(0.5)As_(0.5) and 5 J kg~(-1) K~(-1) in Mn_(1.3)Fe_(0.7)P_(0.5)As_(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_(0.5)P_(0.5) is discussed in the terms of both the thermodynamic Maxwell relation and the Clausius-Clapeyron equation.