Magnetocaloric Effect in Flexible, Free-Standing Gadolinium Thick Films for Energy Conversion Applications

This study presents a method of producing thick (i.e., in the mu m range) polycrystalline Gd free-standing flexible films. Preparation is carried out by sputtering on silicon conventional substrates using tantalum as a buffer and capping layer. Magnetic and magnetocaloric properties show good agreement with data from high-purity bulk Gd, and are not altered by substrate removal. Moreover, the free-standing film is flexible and all the relevant magnetic properties (i.e., Curie temperature Tc, saturation magnetization Ms, and isothermal entropy change AS) are preserved under bending (up to a e = +/- 0.78% strain over the two film sides). The technological opportunities heralded by availability of magnetocaloric flexible self-sustaining films are discussed in the conclusions with particular focus on energy-conversion applications (i.e., cooling and thermal energy harvesting). More precisely, the output-power upper bound of an thermal-energy harvester deploying a Gd flexible film with the reported properties is worked-out using a thermal switch model presented elsewhere. The calculations show a potential output able to supply the new generation of IoT wireless devices as well as small medical implants. The result moot Gd free-standing flexible films as a benchmark for a new generation of small high-throughput magnetocaloric energy-conversion devices.

Automated summary

This study introduces a method for producing polycrystalline Gd free-standing flexible films, while investigating their magnetic and magnetocaloric properties. The results show the stability of these properties even under bending, with potential applications in energy conversion for IoT devices and medical implants.