Understanding magnetocaloric and electrocaloric effects using epitaxial films

需要更节能的制冷，以减少当今生活方式对环境的影响。基于无扩散变换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，即施加电场或磁场导致温度变化的材料。在薄膜的形状上，这种材料可用于微电子或微机械设备中的芯片上铁性冷却。我们实验项目的主要目标是在微观结构水平上了解铁性冷却，特别是磁滞损耗。作为一个合适的模型系统，我们使用外延生长的薄膜，这使得详细的静态和动态研究成为可能。这个一揽子项目结合了磁热薄膜和电热外延薄膜的专业知识。我们的目标是用一个自适应的概念来描述局域结构，这一概念已经成功地应用于等结构磁性形状记忆合金。我们将扩展这一概念来描述磁场循环过程中的滞后损耗，因为假设这种损耗与马氏体微结构中的粗化过程密切相关。特别是，将与SPP的其他参与者密切合作，利用先进的局部以及积分探头来研究导致热量效应的相变。外延异质结构将被用来调节这些材料中的应变，从而允许改变热学性质。类似的方法将被用来研究异质结构中的多热效应。从这个一揽子项目中对电热和磁热材料的直接比较中，我们期望对铁水冷却过程中的基本过程有一个统一的描述。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性冷却的关键参数，这将为进一步优化潜在应用的材料和器件结构奠定基础。

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.