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Theory of X-ray Absorption Spectra and Spin Transfer Torque

<p>The subjects of the thesis are theoretical first principles calculations of X-ray absorption (XA) spectra and current induced spin transfer torque. XA spectra calculated from atomic multiplet theory and from band structure calculations, based on density functional theory for La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> have been compared to experiment. The comparison shows that the effect of the core hole created in the XA process must be considered in the calculation. The theory by Mahan, Nozières and De Dominicis (MND) of dynamical core hole screening is generalised to multiband systems and implemented in first principle calculations. Calculations of the XA spectrum of graphite, including dynamical core hole screening, are shown to better reproduce the relative intensity of the peaks in the experimental spectrum compared to static calculations based on the local density of state of a core excited atom. In combination with experiments the developed method to calculate XA spectra is used to investigate the electronic structure of mixed valent Yb, hydrogen storage in carbon nanotubes and the structure of liquid water. Moreover, a method to calculate the current induced spin transfer torque in materials with a helical spin density wave from first principles has been developed. The method is applied to rare earth metals and it is shown that a current along the axis of spin rotation induces a torque which gives rise to a rotation of the magnetisation direction.</p>

Identiferoai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-6685
Date January 2006
CreatorsWessely, Ola
PublisherUppsala University, Department of Physics, Uppsala : Acta Universitatis Upsaliensis
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, text
RelationDigital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 158

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