Revealing Exchange Interactions in Magnetic Bilayers at the Atomic Scale

本项目由材料研究部电子与光子材料计划（Electronic and Photonic Materials Program，简称EMPs）和凝聚态物理计划（Condensed Matter Physics Program，简称CMP）共同资助。技术描述：本项目旨在探索和揭示磁性双层系统中原子尺度下的磁交换相互作用机制。它包括三个研究部分：1）与磁性层接触的正常非磁性材料的磁极化率; 2）交换偏置的基本起源; 3）磁性双层系统中长程相互作用的影响。在所有情况下，空间变化是特别感兴趣的，作为交换相互作用可能强烈依赖的函数。采用分子束或脉冲激光外延技术制备双层超薄膜。在材料合成步骤之后，使用自旋极化扫描隧道显微镜技术研究了双层系统。磁，电子，和地形信息下到原子尺度的同时获得恒定电流图像和微分电导数据，通过使用磁性探针尖。与理论计算相比，该结果可以为这些重要的、技术上有影响力的材料系统的基本原理提供新的见解。非技术说明：为了进一步简化设备，对基础物理有基本的了解至关重要。一种称为交换耦合的普遍现象是当今最先进的磁性器件技术的核心。一个重要的例子是交换偏置，其中两种类型的薄磁层-铁磁层和反铁磁层-直接接触。这会导致一种独特的行为，称为滞后位移，并增加了一个参数，称为矫顽力。这些效应是现代高密度读头技术的基础;但是尽管有许多理论来解释它，它的最终起源仍然是一个谜。在这个项目中，通过采用具有原子尺度分辨率的磁敏感探针技术，科学家们的目标是解开交换耦合效应，并希望提供新的见解，这可能对未来的磁性技术产生重要影响。该项目还旨在为从K-12到博士的学生提供关键的教育和推广机会。水平本科生和研究生都积极参与该项目的各个阶段，成为未来的科学家。与此同时，开展了两项新的外联活动-一项涉及K-12学校的演讲，另一项涉及K-12学生的课后大学校园活动-其总体目的是激励东南部俄亥俄州的儿童追求科学和工程职业道路。

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) and Condensed Matter Physics Program (CMP) in the Division of Materials Research (DMR).Technical Description: This project is aimed at exploring and revealing magnetic exchange interaction mechanisms in magnetic bilayer systems down to atomic scale. It includes three research components: 1) magnetic polarizability of normally non-magnetic materials in contact with magnetic layers; 2) fundamental origins of exchange bias; and 3) effects of long-range interactions in magnetic bilayer systems. In all cases, spatial variations are of particular interest, as a function of which exchange interactions may depend strongly. Bilayer ultra-thin films are prepared using either molecular beam or pulsed laser epitaxy. Following the materials synthesis step, the bilayer systems are studied using the technique of spin-polarized scanning tunneling microscopy. Magnetic, electronic, and topographical information down to the atomic scale is obtained simultaneously from constant current images and from differential conductance data by using magnetic probe tips. Comparing to theoretical calculations, the results can provide new insights into the fundamentals of these important and technologically impactful material systems.Non-technical Description: In order to miniaturize devices further and further, it is critical to have fundamental understanding of the underlying physics. A general phenomenon called exchange coupling is at the heart of the most advanced magnetic device technologies today. An important example is exchange bias, in which two types of thin magnetic layers - a ferromagnetic and an antiferromagnetic layer - are put into direct contact. This can result in a unique behavior called hysteresis shift and increases in a parameter called the coercivity. These effects underlie modern high-density read head technology; but despite many theories designed to explain it, its ultimate origins remain a mystery. In this project, by employing a magnetically sensitive probe technique having atomic-scale resolution, scientists aim to unravel exchange coupling effects, and hopefully to provide new insights which can have important impacts on future magnetic technologies. The project also aims to provide key educational and outreach opportunities for students ranging from K-12 through the Ph.D. level. Both undergraduate and graduate students are active participants in all phases of the project, on their way to becoming future scientists. At the same time, two new outreach activities are undertaken - one involving presentations in K-12 schools, the other involving after-school, university-campus activities for K-12 students - whose overall purpose is to inspire the children of Southeast Ohio to pursue science and engineering career paths.