Novel caloric materials by mastering hysteresis: microscopic understanding by element-specific studies

掌握滞后现象的新型热量材料：通过特定元素研究的微观理解

• 批准号: 227071330
• 负责人: Professor Dr. Heiko Wende
• 金额: --
• 依托单位: Forschungsgruppe Experimentalphysik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/227071330?language=en
• 关键词: Novel; caloric; materials; mastering; hysteresis

The origin of the magnetocaloric effect, i.e. a reversible temperature change in a suitable material caused by a magnetic field, shall be revealed on a microscopic lengthscale bridging the results determined by commonly employed macroscopic thermodynamic measurements and theory investigations.We will focus on ternary and quaternary Heusler alloys like Ni2MnSn, Ni2MnInxCo1-x, but also on La(Fe1-xSix)13-based compounds, Mn-Fe-P-Si compounds with hexagonal Fe2P-type structure and Mn3GaC systems exhibiting giant magnetocaloric effects. In these cases, the magnetocaloric effect is accompanied by a structural phase transition and all the systems may exhibit different temperature dependencies of magnetic and structural properties for the different elements along the ferroic transition. The X-ray absorption spectroscopy offers the unique possibility to measure spin and orbital magnetic moments, changes in the electronic structure and crystal structure as static properties as well as dynamic properties like lattice vibrations element-specifically. In addition, the Mössbauer spectroscopy will be used for Fe-containing systems to characterize the local structural and magnetic properties. With this approach, we plan to study the relation between (spin resolved) electronic structure and the magnetocaloric effect, the contributions of the lattice vibrations to the total entropy, the temperature-dependence of spin and orbital magnetic moments, and verify the relevant microscopic degrees of freedom relevant for the order character of the transition by comparing our temperature-dependent spectroscopies to theoretical results.

磁热效应的起源，即由磁场引起的适当材料中的可逆温度变化，应在微观长度尺度上揭示，桥接常用宏观热力学测量和理论研究确定的结果。我们将重点关注三元和四元 Heusler 合金，如 Ni2MnSn、Ni2MnInxCo1-x，但也 La(Fe1-xSix)13基化合物、具有六方Fe2P型结构的Mn-Fe-P-Si化合物以及表现出巨磁热效应的Mn3GaC体系。在这些情况下，磁热效应伴随着结构相变，并且所有系统都可以沿着铁性转变表现出不同元素的磁性和结构特性的不同温度依赖性。 X 射线吸收光谱为测量自旋和轨道磁矩、电子结构和晶体结构的静态特性以及晶格振动等动态特性提供了独特的可能性。此外，穆斯堡尔谱将用于含铁系统，以表征局部结构和磁性。通过这种方法，我们计划研究（自旋分辨）电子结构与磁热效应之间的关系、晶格振动对总熵的贡献、自旋和轨道磁矩的温度依赖性，并通过将我们的温度依赖性光谱与理论结果进行比较来验证与跃迁有序特征相关的相关微观自由度。