Magnetic garnet thin films: novel properties through interface and site occupancy engineering

非技术概述铁石榴石是一类具有广泛有用磁性的氧化物材料，使其成为下一代固态存储器和逻辑器件的候选对象，在这些器件中，通过改变石榴石的磁化方向来存储和处理数据。生长铁石榴石薄膜的工艺的发展引起了人们的极大兴趣，但这项工作的绝大多数涉及成分简单的单层石榴石薄膜。这就留下了几个有趣的问题没有得到回答，这些问题构成了这项提案的核心。首先，该提案将解决由不同成分的层组成的多层石榴石薄膜可能产生的磁性，每一层都有几个原子厚。第二，晶体中原子的类型是否可以在原子尺度上控制和排列，以及这种有序产生了什么磁性。第三个耐人寻味的问题是，天然的绝缘体--铁石榴石能否具有导电性，这将有助于对石榴石制成的数据存储设备进行电子读取和写入。该项目开发的技术发现和新材料能力将有助于磁记忆、逻辑和其他薄膜器件的开发，并将发表并传达给工业研究人员。研究生和本科生，包括来自当地社区大学的学生，将接受材料设计、生长和表征方面的培训。这项研究的结果将被纳入课程作业和免费在线科目，一项公共推广活动，以及旨在增加多样性的暑期项目。氧化物异质结构中的占位和界面工程为控制复合氧化物薄膜的性质和揭示新的薄膜现象提供了一个巨大的机会。然而，目前对氧化物异质结构的研究主要集中在钙钛矿结构上，而对石榴石氧化物异质结构的研究较少。该方案开发了薄膜磁性石榴石超晶格、在晶胞内具有两个或两个以上稀土离子有序的石榴石薄膜，以及导电石榴石薄膜。这些薄膜结构将有助于引入电控磁性、多铁性堆栈、电荷和离子传导路径，以及对称性破缺所促进的新的磁性行为。这种新的材料性能可以构成磁记忆、逻辑和其他薄膜器件的基础。更广泛的影响包括对研究生和本科生的培训，工业和公共宣传，在线教学，以及参与旨在增加多样性的暑期项目。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY Iron garnets are a class of oxide material with a wide range of useful magnetic properties, making them candidates for next generation solid-state memory and logic devices in which data is stored and manipulated by changing the magnetization direction of the garnet. The development of processes to grow thin films of iron garnets has led to an explosion of interest, but the great majority of this work involves single layer garnet films of simple compositions. This leaves several interesting questions unanswered, which form the core of this proposal. First, the proposal will address what magnetic properties can emerge from a multilayer garnet film made up of layers of different composition each a few atoms thick. Second, whether the type of atoms in the crystal can be controlled and arranged on the atomic scale, and what magnetic properties emerge from this ordering. An intriguing third question is whether iron garnets, which are naturally insulators, can be grown with electrical conductivity, which would facilitate electrical reading and writing of a data storage device made of garnet. The technical findings and the new material capabilities developed in this project will contribute to the development of magnetic memory, logic and other thin film devices and will be published and communicated to industrial researchers. Graduate and undergraduate students, including from a local community college, will be trained in materials design, growth and characterization. Results from the research will be incorporated into coursework and free online subjects, a public outreach activity, and into summer programs designed to increase diversity. TECHNICAL SUMMARY Engineering of site occupancy and interfaces in oxide heterostructures presents a tremendous opportunity to manipulate the properties of complex oxide thin films and to reveal new thin film phenomena. However, most work on oxide heterostructures has focused on perovskites, and there is little work on garnet oxide heterostructures. This proposal develops thin film magnetic garnet superlattices, garnet films with ordering of two or more rare earth cations within the unit cell, and conductive garnet films. These thin film structures will facilitate the introduction of electrically-controlled magnetic properties, multiferroic stacks, charge and ion conduction pathways, and new magnetic behavior promoted by symmetry breaking. The new material capabilities could form the basis of magnetic memory, logic and other thin film devices. Broader impacts include training of graduate and undergraduate students, industrial and public outreach, online teaching, and participation in summer programs designed to increase diversity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.