CAREER: Hexagonal Ferrite Thin Films for the High-Temperature Magnetoelectric Memory Effect

非技术概述电场和磁场之间的动态耦合-电磁波-的发现和利用给人类社会带来了革命性的变化，特别是在无线通信方面。材料中电场和磁场之间的“静态”耦合（例如，使用电场切换磁体的北极和南极）预计将在紧凑和节能的信息存储和处理，传感器和致动器中具有主要应用。这些应用是期望的，因为对信息存储和处理的需求不断增加，而当前技术的能力正在耗尽。这个教师早期职业发展（CAREER）项目探索了新材料（如六角铁氧体）中电场和磁场之间可能的静态耦合，通过阐明它们的电，磁和结构特性之间的联系，并使用先进的材料制备微调材料。结合本研究，本项目的教育目标是，通过使本科生接触前沿研究和开发以学生为中心的新教学方法来促进基础物理教学，通过系统的创新研究培训来指导和激励学生研究人员，并鼓励K-12学生激发他们对科学的兴趣。（磁电记忆效应）--一种可以作为下一代信息处理和存储技术的工作原理的效应--不幸的是在已知材料中很少，并且限于低温。该学院早期职业发展（CAREER）项目通过发现新材料或通过实验调整已知材料的特性，探索在高温下有效且稳定的磁电记忆效应。特别是，本项目研究了在同时表现出不正常铁电性和不正常铁磁性的材料中可能存在的磁电记忆效应，例如六方晶系铁氧体（h-RFeO 3; R =Y，Ho，Lu）。具体的研究目标是：1）阐明六方晶系铁氧体磁有序的起源。2)实验确定磁电效应，并确定在六角铁氧体的基本机制。3)利用外延薄膜生长技术，通过调整六方晶系铁氧体的结构来调节其磁性能以及磁性能和电性能之间的耦合。采用脉冲激光沉积法制备了具有调谐结构的单晶外延薄膜材料。磁，电子和晶格结构的细节进行了研究，分别使用中子散射，X射线光谱，和X射线衍射。通过测量铁磁性质在电场中的变化，研究了电、磁性质之间的耦合。该项目的成功不仅可以从总体上加深对复合氧化物中磁电耦合的理解，而且还可以在实验上建立一种新的由反常铁电性和反常铁磁性引起的磁电效应的范例

NON-TECHNICAL SUMMARYThe discovery and utilization of the dynamic coupling between the electric and magnetic fields - electromagnetic waves - has revolutionized human society, particularly in the wireless communications. The "static" couplings between the electric and magnetic fields in a material (e.g. switching the north and south poles of a magnet using an electric field) are expected to have major applications in compact and energy efficient information storage and processing, sensors, and actuators. These applications are desired since the demand for information storage and processing is ever increasing while the capabilities of current technology are being exhausted. This Faculty Early Career Development (CAREER) project explores the possible static couplings between the electric and magnetic fields in new materials, such as hexagonal ferrites, by elucidating the connections between their electric, magnetic, and structural properties, and fine-tuning the materials using advanced material preparations. Integrated with the research, the educational objectives of this project are, to promote teaching undergraduate students fundamental physics by exposing them to cutting-edge research and by exploiting new student-centered pedagogical approaches, to mentor and inspire student researchers with systematic trainings for innovative research, and to engage K-12 students to stimulate their interests in science.TECHNICAL SUMMARY Switching a magnetic dipole using an electric field (magnetoelectric memory effect) - an effect that can be a working principle of the next-generation technology for information processing and storage - is unfortunately rare in known materials and restricted to low temperature. This Faculty Early Career Development (CAREER) project explores the magnetoelectric memory effect that is efficient and stable at high temperature, by the discovery of new materials or by tuning the properties of known materials experimentally. In particular, this project investigates the possible magnetoelectric memory effect in the materials that exhibit both improper ferroelectricity and improper ferromagnetism, such as hexagonal ferrites (h-RFeO3; R =Y, Ho, Lu). The specific research objectives of the proposed work are: 1) Elucidate the origin of the magnetic orderings in hexagonal ferrites. 2) Experimentally determine the magnetoelectric effect and identify the underlying mechanism in hexagonal ferrites. 3) Adjust the magnetic properties and the coupling between the magnetic and electric properties in hexagonal ferrites by tuning their structures using epitaxial thin film growth. Pulsed laser deposition method is employed to prepare single crystalline epitaxial thin film materials of tuned structures. The details of magnetic, electronic, and lattice structures are investigated using neutron scattering, x-ray spectroscopy, and x-ray diffraction respectively. The couplings between the electric and magnetic properties are studied by measuring the change of ferromagnetic properties in an electric field. Besides advancing the understanding in the magnetoelectric couplings in complex oxides in general, the success of the project may experimentally establish a new paradigm of magnetoelectric effect originated from improper ferroelectricity and improper ferromagnetism