MATERIALS WORLD NETWORK The Magnetostructural Response in Heterostructured Systems: a US - UK Collaboration

磁性材料在现代社会中无处不在，存在于各种先进设备、传感器和电机中。由于磁力只在很长的距离内失去力量，它允许物理上分离良好的组件之间的通信。这一独特的特性允许将电能转换为机械能，帮助微波设备进行电信、电力传输和分配，实现数据存储系统，并促进对环境条件的感知。自发明磁罗盘(公元前221年秦朝首次报道)以来，人们一直在稳步努力，以定制和优化磁性材料的性能。两千年后，很明显，磁性设备性能的突破性进步将需要新材料和新的设计原则来控制磁性能。在这个项目中，我们将阐明一个重要但鲜为人知的现象的起源，即在由具有强电子-晶格耦合的磁性材料组成的层状系统中，外部控制经典内在参数-磁转变温度的现象。这将由英国利兹大学和STFC卢瑟福·阿普尔顿实验室以及美国东北大学共同开展的跨大西洋研究项目来完成。布鲁克海文国家实验室将作为项目合作伙伴参加。我们将使用在CsCl相中结晶的FeRh作为模型系统：这种材料在升温时经历从反铁磁(AF)到铁磁(F)的相变，通过大约100摄氏度的临界温度，伴随着各向同性的晶格膨胀。除了提供一种具有磁性可以随意开启和关闭的迷人性质的材料之外，关于这种转变的根本机制的深层次问题仍然存在。我们已经证明了在利兹生长这种材料的外延薄膜的能力，我们的美国和英国的研究伙伴已经用SQUID、同步加速器x射线衍射、x射线磁性圆二色谱和偏振中子反射仪对这种内在转变进行了表征。我们现在寻求使用NSF-EPSRC联合支持来巩固这一联系，并进行一些新颖的实验，我们试图使用外部参数来控制AF-F相变。在我们目前所拥有的薄膜中，正如在大体上所知的那样，相边界的位置可以通过精确的FeRh化学计量比来本质上控制。一些诱人的结果出现在文献中，其中通过构建包含磁结构材料的异质结构，这种转变已经受到其他外部参数的相当明显的影响。在这里，我们将通过探索这种异质结构以及FeRh对外部应变、静磁场和交换场的响应来阐明磁结构响应的潜在机制，并寻求将它们结合在一起以相互增强的方法。

Magnetic materials are ubiquitous in modern society, present in advanced devices, sensors and motors of every kind. As the magnetic force loses strength only over very long distances, it allows for communication between components that are physically well-separated. This unique property permits the conversion of electrical to mechanical energy, assists microwave devices in telecommunications, transmission and distribution of electric power, enables data storage systems and facilitates sensing of ambient conditions. Steady effort has been extended since the invention of the magnetic compass (first reported in the Qin Dynasty, 221 BC) to tailor and optimize magnetic materials' performance. Two thousand years later it is clear that breakthrough advances in the performance of magnetic devices will require new materials and novel design principles to control magnetic performance. In this project we will clarify the origins of a significant but poorly-understood phenomenon of extrinsic control of a classically intrinsic parameter - the magnetic transition temperature - in layered systems comprised of magnetic materials with strong electron-lattice coupling. This will be done by a joint transatlantic programme of research between the University of Leeds and STFC Rutherford Appleton Laboratory in the UK, and Northeastern University in the USA. Brookhaven National Laboratory will participate as a project partner. We shall use FeRh, which crystallizes in the CsCl phase, as a model system: this material undergoes a phase transition from antiferromagnetic (AF) to ferromagnetic (F) on warming through a critical temperature that is conveniently located at about 100 degrees Celsius, accompanied by an isotropic lattice expansion. As well as providing a material with the fascinating property that magnetism can be switched on and off at will, deep questions about the underlying mechanism for the transition remain.We have already demonstrated the capability to grow epitaxial thin films of this material in Leeds and the intrinsic transition has been characterized by SQUID, synchrotron x-ray diffraction, x-ray magnetic circular dichroism, and polarised neutron reflectometry by our research partners in the USA and UK. We now seek to use joint NSF-EPSRC support to cement this link, and carry out some novel experiments where we seek to control the AF-F phase transition using extrinsic parameters. In the films we have at present, as is known in the bulk, the position of the phase boundary can be controlled intrinsically by the exact FeRh stoichiometry. A few tantalising results are present in the literature where the transition has been quite markedly affected by other external parameters by building heterostructures incorporating magnetostructural materials. Here we will throw light on the underlying mechanism for the magnetostructural response by exploring such heterostructures and the response of the FeRh to extrinsic strain, magnetostatic and exchange fields, and seek ways in which they might be combined to enhance each other.