Temperature Dependence of Antiferromagnetic Coupling in Perpendicularly Magnetized [Pd/CoFeB]_N/Ru/[CoFeB/Pd]_N Structures

Yili Xiao

ABSTRACT:

Synthetic antiferromagnetic (SAF) structures, which involve the oscillatory interlayer exchange coupling between ferromagnetic layers separated by a nonmagnetic metal spacer, have wide ranging applications in magnetic sensors, non-volatile memory, and magnetic recording media. The exchange coupling strength is a function of spacer thickness, material, interface conditions, and temperature. Investigation of its temperature dependence, and that of the overall switching behavior is not only essential for applications of the SAF system in magnetic devices, but also provides valuable insight to the underlying mechanism of interlayer magnetic coupling.

Numerous experimental and theoretical investigations have been carried out on the temperature dependent behavior of interlayer coupled structures. Proposed mechanisms of temperature dependence include smearing of the Fermi surface, thermal spin wave excitation and magnetostatic Neel coupling. However, most of the work on temperature dependence was focused on SAF structures with an in-plane magnetic anisotropy. Although interlayer exchange coupling is traditionally regarded as an interfacial effect, it has recently been reported that magnetic anisotropy also affects the interlayer coupling behavior in [Pt/Co]5/Ru/[Co/Pt]5 multilayered systems. In this report, I will present some of our experimental results on the temperature dependent behavior in AF coupled, perpendicularly magnetized [CoFeB/Pd]N multilayers. Current results suggest quite different temperature dependence of the interlayer coupling strength compared with in-plane CoFeB/Ru/CoFeB systems. A systematic study involving various experimental and structural parameters is carried out in an effort to clarify the mechanism of such behaviors.

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Introduction to Meta-material and Its Application

Wei Shi

Department of Optical Science and engineering, Fudan University

Abstract

Meta-materials are artificial materials engineered to have properties that may not be found in nature. They are assemblies of multiple individual elements fashioned from conventional microscopic materials such as metals or plastics, but the materials are usually arranged in periodic patterns. Meta-materials gain their properties not from their composition, but from their exactingly-designed structures. Their precise shape, geometry, size, orientation and arrangement can affect the waves of light or sound in an unconventional manner, creating material properties which are unachievable with conventional materials. These meta-materials achieve desired effects by incorporating structural elements of sub-wavelength sizes, i.e. features that are actually smaller than the wavelength of the waves they affect.

The primary research in metamaterials investigates materials with negative refractive index. Negative refractive index materials appear to permit the creation of superlenses which can have a spatial resolution below that of the wavelength. In other work, a form of 'invisibility' has been demonstrated at least over a narrow wave band with gradient-index materials. Although the first metamaterials were electromagnetic, acoustic and seismic metamaterials are also areas of active research.

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Photoluminescence of ZnO nanorod-TiO₂ nanotube hybrid arrays

prepared by electrodeposition

Hua Cai

Department of Optical Science and Engineering, Fudan University

Abstract

Recently, the research of vertically oriented, highly ordered TiO₂ nanotube arrays (TiO₂ NTs) was becoming of importance in a variety of fields, such as fabrication of dye-sensitized solar cells (DSCCs) and environmental protection, and received considerable attention. The aligned uniform nanotube structure dramatically improved charge transport properties, which greatly contributed to the superior photoelectrochemical performance.

As another promising heterogeneous photocatalyst, semiconductor ZnO has also been intensively investigated for environmental remediation or photovoltaic devices. The modification of the TiO₂ nanomaterials with other semiconductor could alter the charge transfer properties between the TiO₂ and the surrounding environment. The ZnO nanorods (ZnO NRs) embedded in TiO₂ nanotubes were used as photoelectrochemical reagent. The photoelectrochemical performance could be significantly enhanced on the ZnO/TiO₂ NR/Ts electrode compared with that on pure TiO₂ NTs, since the ZnO possesses an energy band similar to that of TiO₂. The electrons transfer from the conduction band of ZnO to the conduction band of TiO₂, and conversely, the holes transfer from the valance band of TiO₂ to the valance band of ZnO, that give rise to decrease of the pairs’ recombination rate.

In this presentation, I will firstly give a brief introduction of ZnO/TiO₂ composite structure, including its synthesis methods, transportation mechanism of electron and applications. Then, my own work on the photoluminescence(PL) and morphology of this structure will be mainly discussed.

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