Understanding magnetocaloric and electrocaloric effects using epitaxial films

需要更节能的制冷来减少当今生活方式对环境的影响。基于无扩散相变的固态制冷是一种很有前途的解决方案。在我们的联合项目中，我们专注于表现出电热或磁热效应的材料，即电场或磁场的应用导致温度变化的材料。在薄膜的形状中，这种材料可以用于微电子或微机械设备中的片上铁电冷却。我们的实验项目的主要目标是了解铁电冷却，特别是在微观结构水平上的磁滞损耗。作为一个合适的模型系统，我们使用外延生长的薄膜，使详细的静态和动态的研究。该项目结合了磁热薄膜和电热外延薄膜的专业知识。我们的目标是描述的局部结构与自适应的概念，我们已经成功地应用于同构磁性形状记忆合金。我们将扩大这一概念的滞后损失的描述，因为它是假设，这种损失是密切相关的马氏体微观结构中的粗化过程。特别是，相变，导致热量的影响，将与先进的本地以及与其他参与者密切合作，在SPP积分探头进行研究。外延异质结构将用于调整这些材料中的应变，这允许修改热性能。类似的方法将被用来研究异质结构中的多热量效应。从直接比较电和磁热材料在这个包项目中，我们期望一个统一的描述铁电冷却过程中的基本过程。我们的基础研究将伴随着间接和直接的测量，以量化冷却周期中的温度变化。我们的基础研究结果将使我们能够确定更有效的铁电冷却的关键参数，这将是进一步优化潜在应用的材料和器件结构的基础。

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.