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膜和纳米结构的性质。虽然交换耦合和巨磁电阻等静态行为受到了最大的关注，但在理解这些材料的动力学行为方面也有重要的问题。在这一领域，提出了三项研究。(1)交换耦合磁性多层膜的动态行为。这将通过铁磁共振方法在低场下进行研究。与研究得很好的磁性多层膜中的磁共振情况不同，这一区域被称为反共振条件--皮肤深度变大，材料“打开”--尚未被研究。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有很大的不同，而且这种效应在技术上有重要的应用。此外，我们打算研究在一些磁性多层膜中发生的非常强的低场吸收。(2)层状结构中交换耦合强度变化的研究。现在已经测量了许多材料组合的两个铁磁体之间通过非磁性间隔材料的交换耦合强度的测定。相反，这种交换耦合强度的变化还没有得到解决，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。这将适用于金属多层膜和铁磁/反铁磁结构，在这些结构中，界面粗糙度可能会在交换耦合中产生很大变化。(3)超小图形结构的动力响应。这将包括对超小(直径10 nm)磁点阵列以及单材料点(Fe和坡莫合金)和多层(Fe/Pd和Co/Pd)点的动态测量。Co/Pd点特别有趣，因为可以通过改变层的厚度来将磁化强度从面内改变到面外。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模沉积)、点分离和点结构。这些措施对磁记忆技术将是重要的。国际和平研究所都有将教育与研究相结合以及促进多样性的已证明的历史，这一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具有尖端技术的基本实验技术培训。这项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。层状磁性材料领域在过去十年中异常活跃。巨磁电阻等重要发现已经在计算机存储器中实现，导致磁硬盘系统的显著改进。该项目将包括对这些新的层状材料的研究，以探索基础物理和可能的应用。第一项研究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，该材料拒绝电磁波。这一功能还没有经过实验测试，尽管它在高频信号处理方面具有重要的技术前景。磁性多层膜将被制造和测试，以确定这是否如预测的那样起作用，以及它在技术上是否可行。第二个主要主题是关于这些层状材料中的磁耦合。特别令人感兴趣的是，这种耦合是如何沿层的不同位置变化的。这一点很重要，因为这种变化在上述高频响应中起着重要作用。最后一个项目涉及超小磁点。这些超小的点的直径只有50个原子左右，所以它们的性质可能与我们日常处理的材料非常不同。实验将研究改变网点的形状以及分层图案如何改变这些网点的磁化方向。这对于磁记录可能非常重要，因为这些微小的点阵列可以存储大量的信息。首席调查员在将教育与研究相结合以及促进多样性方面有着良好的历史，这一对教育和人力资源开发的承诺将继续在拟议活动中得到强调。该项目的学生接受严格的物理和材料方面的培训，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.