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 technology The 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.
