Understanding magnetocaloric and electrocaloric effects using epitaxial films

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There is a need for more energy-efficient refrigeration to reduce the environmental impact of todays lifestyle. Solid state refrigeration based on diffusionless transformation is a promising solution. Within our joint project we focus on materials exhibiting electrocaloric or magnetocaloric effects, i.e. where the application of an electric or magnetic field leads to a temperature change. In shape of thin films such materials might be used for on-chip ferroic cooling in microelectronics or micromechanical devices. The main goal of our experimental project is to understand ferroic cooling and in particular hysteresis losses on a microstructural level. As a suitable model system we use epitaxially grown films, which enable detailed static and dynamic studies. This package project combines expertise on both, magnetocaloric films and electrocaloric epitaxial films. We aim to describe the local structure with an adaptive concept, which we already successfully applied for isostructural magnetic shape memory alloys. We will expand this concept for the description of hysteretic losses during field cycling as it is postulated that such losses are closely connected to coarsening processes in the martensitic microstructure. In particular, the phase transformation, which leads to the caloric effects, will be studied with advanced local as well with integral probes in close collaboration with other participants in the SPP. Epitaxial heterostructures will be used to tune the strain in these materials, which allows modifying caloric properties. Similar approaches will be utilized to study multicaloric effects in heterostructures. From the direct comparison of electro- and magnetocaloric materials within this package project we expect a unified description of the underlying processes during ferroic cooling. Our fundamental studies will be accompanied by indirect and direct measurements to quantify the temperature change during a cooling cycle. The results of our fundamental investigations will enable us to identify the key parameters for more efficient ferroic cooling, which will be the basis for a further optimization of materials and device structures for potential applications.