Specific heat and entropy change at the first order phase transition of La(Fe-Mn-Si)_(13)-H compounds

摘要

In this paper, we present the results of an experimental investigation on the magnetocaloric properties of hydrogenated La(Fe-Mn-Si)_(13)-H with Mn substituting Fe to finely tune the transition temperature. We measured the specific heat under magnetic field c_p(H, T) and the magnetic field induced isothermal entropy change Δs(H, T) of a series of compounds by direct Peltier calorimetry. Results show that increasing Mn from 0.06 to 0.46 reduces the transition temperature from 339 K to 270 K whilst the total entropy change due to a 1.5 T field is depressed from 18.7 J kg~(-1)K~(-1) to 10.2 J kg~(-1) K~(-1) and the thermal hysteresis similarly is reduced from 1.5 K to zero. In the paper, we interpret the results in terms of a magnetic phase transition changing from the first to the second order with increasing Mn content, and we discuss the value of the results for magnetic cooling applications.