Anisotropic magnetocaloric effect in gadolinium thin films: Magnetization measurements and acoustic detection

Abstract

In this letter, it is demonstrated the ability of the magnetoacoustic technique in detecting the magnetocaloric effect in gadolinium thin films (1.0 μm and 3.0 μm thick), which is not accessible through conventional temperature sensors because of the reduced mass of the samples. The method, which detects the direct effect of the sample temperature variation, proved to be sensitive to the anisotropy of the films, making possible for the investigation of the anisotropic magnetocaloric effect. Magnetization measurements were also carried out, and from these measurements both the adiabatic temperature and the isothermal entropy variations were calculated. The acoustically detected magnetocaloric effect shows very good agreement with these calculations.

Acoustic Detection of the Magnetocaloric Effect in Gadolinium Thin Films: Influence of the Substrate

“…Indeed, we reported recently results on Gd thin films grown on fused quartz substrates [8]. Very good agreement between the acoustic signal behavior and magnetization measurements was found.…”

“…1 of Ref. [8], the magnetization along the film plane exceeds the perpendicular one, particularly at moderate external fields. As a consequence, the MCE also depends on the film orienta- tion with respect to the applied magnetic field.…”

“…[8], a calibration procedure allows us to retrieve the adiabatic temperature variation using the magnetoacoustic data, despite the fact that heat flows out of the magnetic film during these measurements. Such a calibration is possible because both the magnetoacoustic signal and the adiabatic temperature change are proportional to the amount of energy supplied by the application of the magnetic field, which is a function of the magnetic field itself and of the temperature.…”

“…Nonetheless, the values for the adiabatic temperature change can be retrieved from the magnetoacoustic measurements after an appropriate normalization procedure, as pointed out in Ref. [8].…”

Temperature dependent low-field measurements of the magnetocaloric ΔT with sub-mK resolution in small volume and thin film samples

“…However, only data for a single sample temperature and increasing external fields were shown. 6 Here, we show temperature dependent measurements of the MCE in small volume samples and a Gd thin film with a thickness of 1.4 lm. A relative error of the measured temperature change of better than 0.3 mK is obtained.…”