Direct observation of magnetocaloric effect by differential thermal analysis: Influence of experimental parameters

Abstract

The magnetocaloric effect is the isothermal change of magnetic entropy and the adiabatic temperature change induced in a magnetic material when an external magnetic field is applied. In this work, we present an experimental setup to study this effect in metamagnetic transitions, using the differential thermal analysis technique, which consists in measuring simultaneously the temperatures of the sample of interest and a reference one while an external magnetic field ramp is applied. We have tested our system to measure the magnetocaloric effect in La 0.305 Pr 0.32 Ca 0.375 MnO 3 , which presents phase separation effects at low temperatures (T < 200 K). We obtain ∆T vs H curves, and analyze how the effect varies by changing the rate of the magnetic field ramp. Our results show that the intensity of the effect increases with the magnetic field change rate. We also have obtained the effective heat capacity of the system without the sample by performing calorimetric measurements using a pulse heat method, fitting the temperature change with a two tau description. With this analysis, we are able to describe the influence of the environment and subtract it to calculate the adiabatic temperature change of the sample. Introduction.Since de observation of magnetocaloric effect (MCE) near room temperature in 1997 by Pecharsky et al i an important increase in the amount of work in that topic has been observed. Most of the work has been devoted to obtain a large MCE around room temperature using the most stable, cheapest and easy-to-obtain material. In that sense, materials belonging to different kinds, such as intermetalic compounds, rare earth metals and alloys and manganites were proposed as possible alternatives. But, as the complexity of the systems growths, a more careful interpretation of the relation between the magnetization results and the MCE is needed.

Grain size modification in the magnetocaloric and non-magnetocaloric transitions in La0.5Ca0.5MnO3 probed by direct and indirect methods

“…In all the cases the sample was zero field cooled to the target temperature and then the field was applied with a constant rate of 200 Oe/sec. and the heat exchanged with the environment has been taken into account 30 .…”