Flexible, Free-Standing Gadolinium Thick Film For Energy Conversion Applications

Magnetocaloric materials have been intensely studied, for more than twenty years, as solid-state refrigerant in cooling applications. This paved the way to a wider technological framework, in the field of energy conversion, with particular focus on microelectromechanical systems (MEMS). Indeed, these materials in the form of freestanding thin layers offer the opportunity to use the magnetocaloric effect in micro-coolers, and its corollary, the pyromagnetic effect, in microgenerators. An example of microgenerator design is given in Fig. 1 (left) where the active material (i.e. the Gd film, green line) moves between a patterned magnet on the top and the heat sink on the bottom. In this framework we produced freestanding layers of Gadolinium (17 μm thick, 35 × 35 mm2) [1] which present magnetic and magnetocaloric properties close to high-purity bulk Gd (Fig.1 center) [2]. Moreover, the freestanding film is flexible (Fig.1 right) and all the relevant magnetic properties (i.e., Curie temperature Tc, saturation magnetization Ms, and isothermal entropy change) are preserved under bending (up to a ϵ = ±0.78% strain over the two film sides). The films presented here exhibit all the functional properties needed to become a benchmark for the application of magnetocaloric materials as active components in micro-systems for energy recovery.