Elasticity of ferroic and multiferroic materials: a new UK facility for Resonant Ultrasound Spectroscopy with applied magnetic field up to 14 Teslas

本课题福尔斯属于材料物理领域，主要包括两个部分。在初始阶段，将建立一个新的仪器来测量小样品的弹性刚度，小到~1mm^3。该仪器将基于共振超声光谱（罗斯）的原理，其中单晶或多晶样品以接近1 MHz的频率振动。与音叉或钟的振动方式完全相同，振动频率取决于材料的弹性刚度和物体的形状。如果物体包含缺陷，类似于钟的裂缝，一些振动能量被耗散，共振被加宽。样品的共振可以在低温和高温下测量，因此，已知形状的物体的弹性特性可以在其内部发生任何能量耗散的同时确定。这些特性对晶体结构的变化特别敏感，这可能与电偶极子或磁偶极子的发展有关。新仪器将特别增加一个强磁体，以便可以研究属于“铁性”和“多铁性”相的材料的特性，作为温度和磁场强度的函数。该项目的第二部分涉及在一系列材料的合作研究中实施新的罗斯仪器，这些材料开发出对商业设备应用具有潜在重要性的特性，例如超导体、自旋电子学和磁电存储器。这些性质发展的基本原理是（a）它们产生于晶体结构和/或电子结构的细微变化，（B）它们强烈依赖于温度和磁场强度，（c）它们与应变状态的变化有关，因此与弹性常数的大变化有关，（d）它们几乎总是与特定类型的缺陷的发展有关，例如相变孪壁，这导致材料在亚微观长度尺度上变得不均匀，以及（e）这种缺陷具有它们自己的结构，电磁特性特别的优点是，罗斯方法提供了一种高灵敏度的方法，用于测量与相变相关的缺陷响应于外部施加的场而移动的的程度。此外，新仪器将允许对毫米大小的电子设备进行无损检测，这些设备依赖于对磁场敏感的组件，并有可能测量纳米材料的弹性。

This project falls in the field of materials physics and contains two parts. In the initial phase, a new instrument will be built to measure the elastic stiffness of small samples, down to ~1mm^3. The instrument will be based on the principle of Resonant Ultrasound Spectroscopy (RUS) in which a single crystal or polycrystalline sample is caused to vibrate at frequencies close to 1 MHz. In exactly the same manner as a tuning fork or a bell, the vibration frequencies depend on the elastic stiffness of the material and the shape of the object. If the object contains a defect, analogous say to a crack in a bell, some of the vibration energy is dissipated and the resonances are broadened. Resonances of the sample can be measured at low temperatures and at high temperatures so that the elastic properties of an object of known shape can be determined simultaneously with any energy dissipation which occurs within it. These properties are particularly sensitive to changes in crystal structure which might be associated with the development of electric or magnetic dipoles. The new instrument will have the special addition of a strong magnet so that the properties of materials belonging to the topical classes of "ferroic" and "multiferroic" phases can be investigated as functions of both temperature and magnetic field strength. As such it will provide a unique and medium/long term contribution to the science infrastructure of the UK.The second part of the project involves implementation of the new RUS instrument in a series of collaborative studies of materials which develop properties that are potentially important for application in commercial devices involving, for example, superconductors, spintronics and magnetoelectric memories. The principles underpinning the development of these properties are (a) that they arise from subtle changes in crystal structure and/or electronic structure, (b) that they are strongly dependent on temperature and magnetic field strength, (c) that they are associated with changes in strain state and, hence, with large changes in the elastic constants, (d) that they are almost invariably associated with the development of specific types of defects, such as transformation twin walls, which cause the materials to become heterogeneous on a submicroscopic length scale and (e) that such defects have their own structural, electric and magnetic properties. Particular advantage will be taken of the fact that the RUS method provides a highly sensitive method for measuring the extent to which transformation-related defects are mobile in response to an externally applied field. In addition, the new instrument will allow non-destructive testing of mm-sized electronic devices which depend on components that are sensitive to magnetic fields, and the possibility of measuring elastic properties of nanomaterials.