What do we know about the magnetocaloric effect, and what we don't?
V.K. Pecharsky, Ames Laboratory and Department of Materials Science and
Engineering, Iowa State University, Ames
Abstract
The relationships between both extensive and intensive properties quantifying the
magnetocaloric effect, i.e. between the isothermal entropy change and the adiabatic
temperature change, respectively, have been analyzed. An extensive measure of the
magnetocaloric effect alone, without considering another important and also extensive
thermodynamic property, i.e. the heat capacity, may lead to biased conclusions about the
size of the magnetocaloric effect and, consequently, about the applicability of a magnetic
material as a magnetic refrigerant. Furthermore, we discuss the relationship between the
behavior of the temperature dependent heat capacity at constant pressure measured in
different magnetic fields and the magnetocaloric effect in magnetic systems with and
without discontinuous change of entropy. It is shown that the two are directly related to
one another, and if the behavior of either property (i.e. the heat capacity or the
magnetocaloric effect) is known, the general behavior of the second one can be predicted.
The derived relationships are illustrated using several sets of experimental data and
model examples.