A Peltier cells differential calorimeter with kinetic correction for the measurement of cp(H, T) and Δs(H, T) of magnetocaloric materials

In this paper we describe and test a setup for the characterization of the magnetocaloric effect around room temperature. The setup is a differential calorimeter able to measure both the specific heat c(p) (H, T) under constant magnetic field H and the isothermal entropy change induced by changing H, Delta s(H, T), in the room temperature range. The setup uses miniaturized Peltier cells to measure the heat flux, with resolution of about 1 mu W, and power Peltier cells to regulate the temperature in the range from 243 K (-30 degrees C) to 343 K (+ 70 degrees C). The kinetic effects due to the heat capacity of the measuring cells are taken into account by a simple model of the heat flux diffusion in the calorimetric cell. As measurement examples, we show the characterization of the magnetocaloric effect in magnetic materials with a second order transition [without latent heat and without hysteresis, as in the La-1(Fe1-x-yCoySix)(13) alloy with x=0.077 and y=0.079] and with a first order transitions (with latent heat and hysteresis as in Ni50Mn36Co1Sn13). As a result we compare the entropy change Delta s(H, T) derived from (i) the integration of the specific heat c(p)(H, T) and (ii) the direct isothermal measurements, obtaining an excellent agreement. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3499253]