RUI: Dynamic Properties of Magnetic Multilayers and Nanostructures

这个凝聚态物理项目的重点是磁性多层和纳米结构的性质。而静态行为，如交换耦合和巨磁电阻已经收到了大部分的关注，有重要的问题在理解这些材料的动态行为以及。在这方面提出了三项研究。(1)交换耦合磁性多层膜的动态特性。这将在低磁场下通过铁磁共振方法进行研究。这个区域，不像在磁性多层膜中磁共振的充分研究的情况，被称为反共振条件——在这种情况下，表皮深度变大，材料“打开”——还没有被研究过。这是令人惊讶的，因为理论计算表明多层膜中的反共振与单层膜中的反共振非常不同，因为这种效应有重要的技术应用。此外，我们打算研究在某些磁性多层膜中发生的非常强的低场吸收。(2)层状结构交换耦合强度变化规律研究。通过非磁性间隔材料测定两个铁磁体之间的交换耦合强度，现在已经对许多材料组合进行了测量。相比之下，这种交换耦合强度的变化尚未得到解决，尽管它在结构的动态特性中起着关键作用。方差将通过使用来自铁磁共振测量的线宽信息来测量。这将用于金属多层和铁磁体/反铁磁体结构，其中界面粗糙度可能会产生很大的交换耦合变化。(3)超小型花纹结构的动力响应。这将包括对超小（直径10纳米）磁点阵列的动态测量，以及单材料点（Fe和Permalloy）和多层（Fe/Pd和Co/Pd）点。Co/Pd点特别有趣的是，通过改变层的厚度，磁化强度可以从面内改变到面外。该项目还将研究点阵列的磁性质量如何取决于制造工艺（离子束蚀刻和通过蛋白质掩膜沉积）、点分离和点结构。这些测量对磁存储技术非常重要。PI都有将教育与研究结合起来以及促进多样性的历史，这种对教育和人力资源开发的承诺将继续在拟议的活动中得到强调。参与该项目的研究生和本科生接受尖端技术的基础实验技术培训。这种培训将为他们在学术界、工业界或政府的一系列职业生涯做好准备。近十年来，层状磁性材料领域异常活跃。诸如巨磁阻等重要发现已经在计算机存储器中实现，导致磁性硬盘系统的重大改进。该项目将包括对这些新型分层材料的研究，以探索基础物理学和可能的应用。这些研究中的第一个涉及这些材料在高频下的电磁响应。理论计算表明，在特定频率下，这种材料拒绝电磁波。该特性尚未经过实验测试，尽管它在高频信号处理方面具有重要的技术前景。磁性多层材料将被制造和测试，看看它是否像预期的那样工作，是否在技术上可用。第二个主要主题涉及这些层状材料中的磁耦合。特别令人感兴趣的是这种耦合如何沿着层的不同位置变化。这很重要，因为这种变化在上述高频响应中起着重要作用。最后一个项目涉及到超小型磁点。这些超小的点直径只有大约50个原子，因此它们与我们日常使用的材料具有非常不同的特性。实验将研究如何改变这些点的形状和分层模式可以改变这些点的磁化方向。这对于磁记录来说是非常重要的，因为这些小点的阵列可以存储大量的信息。主要研究人员在将教育与研究结合起来以及促进多样性方面有着明显的历史，这种对教育和人力资源发展的承诺将继续在拟议的活动中得到强调。该课程的学生接受物理和材料方面的严格培训，可以从事学术或工业科学方面的职业。

This condensed matter physics project focuses on the properties of magnetic multilayers and nanostructures. While static behaviors, such as exchange coupling and giant magnetoresistance have received most of the attention, there are important issues in understanding the dynamical behavior of these materials as well. In this area three studies are proposed. (1) Dynamic behavior of exchange-coupled magnetic multilayers. This will be studied at low fields via ferromagnetic resonance methods. This area, unlike the well studied case of magnetic resonance in magnetic multilayers, is known as the anti-resonance condition - where the skin depth becomes large and the material "opens up" - has not been investigated. This is surprising since theoretical calculations indicate that anti-resonance in multilayers is very different from anti-resonance in single films and because there are significant technological applications for this effect. In addition we intend to investigate a very strong low-field absorption that occurs in some magnetic multilayers. (2) Studies of the variance of exchange coupling strength in layered structures. The determination of th e exchange coupling strength between two ferromagnets through a nonmagnetic spacer material has now been measured for many material combinations. In contrast, the variance in this exchange coupling strength has not been addressed, even though it plays a critical role in the dynamic properties of the structure. The variance will be measures by using linewidth information from ferromagnetic resonance measurements. This will be done for the metallic multilayers and for ferromagnet/antiferromagnet structures where interface roughness is likely to create large variations in exchange coupling. (3) Dynamic response of ultra-small patterned structures. This will include dynamic measurements on ultra-small (10 nm diameter) magnetic dot arrays, and both single material dots (Fe and Permalloy) and multilayer (Fe/Pd and Co/Pd) dots. The Co/Pd dots are particularly interesting in that the magnetization can be changed from in-plane to out-of-plane by changing the thicknesses of the layers. The project will also investigate how the magnetic quality of the dot arrays depends on fabrication process (ion-beam etching and deposition through a protein mask), dot separation, and dot structures. These measurements will be important for magnetic memory technologyThe PI's all have a demonstrated history of integrating education with research as well as promoting diversity, and this commitment to education and human resource development will continue to be emphasized in the proposed activity. Graduate and undergraduate students involved in the project receive training in fundamental experimental techniques with cutting edge technology. This training will prepare them for a range of careers in academe, industry or government.The field of layered magnetic materials has been exceptionally active in the last decade. Important discoveries such as giant magnetoresistance have already been implemented in computer memories, leading to significant improvements in magnetic hard disk systems. The project will include studies of these new layered materials to explore fundamental physics and possible applications. The first of these investigations deals with the electromagnetic response of these materials at high frequencies. Theoretical calculations show that at particular frequencies the material rejects electromagnetic waves. This feature has not been tested experimentally even though it has significant technological promise for high frequency signal processing. Magnetic multilayers will be fabricated and tested to see if this works as predicted and if it is usable technologically. The second main topic deals with the magnetic coupling in these layered materials. Of particular interest is how this coupling varies from position to position along the layers. This is important because this variation plays an important role in the high frequency response described above. The final project deals with ultra-small magnetic dots. These ultra-small dots are only about 50 atoms in diameter so they can have very different properties than materials we deal with on an everyday basis. The experiments will study how varying the shape of the dots as well as the layering pattern can change the magnetization direction in these dots. This could be very important for magnetic recording because an array of these tiny dots could store an enormous amount of information. The Principal Investigators have a demonstrated history of integrating education with research as well as promoting diversity, and this commitment to education and human resource development will continue to be emphasized in the proposed activity. Students in this program receive rigorous training in physics and materials, and can pursue careers in either academic or industrial science.