Determination of the entropy change using the acoustic detection technique in the investigation of the magnetocaloric effect

In this paper we demonstrate the use of the acoustic detection as an alternative way to determine the entropy variation, ΔST, a parameter normally used to characterize the magnetocaloric effect. The measurements were performed for a Gd sample in the 252-316 K temperature range for magnetic fields from zero up to 50 kOe. The reversible adiabatic curves were built in a T versus H diagram, and specific heat data obtained at zero-magnetic field were employed to assign the entropy values of each curve. Subsequently, the entropy was plotted as a function of temperature for fixed magnetic fields, and therefore the isothermal entropy variation, ΔST, was found as a function of the temperature for several magnetic field steps.