Corrente de spins em nanoestruturas metálicas

• Autor(a) principal: Guimarães, Filipe Souza Mendes
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal Fluminense (RIUFF)
• Texto Completo: https://app.uff.br/riuff/handle/1/17283
• topic: Magnetismo; Nanoestrutura metálica; Dinâmica de spins; Bombeamento de spins; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA

The physical mechanisms that control the spin dynamics in nanoscale systems such as magnetic thin films and multilayers are of great importance for the development and improvement of technological applications. Factors that contribute to magnetization relaxation are particularly important to magnetic media writing processes that involve reorientation of a local magnetization. One of those mechanisms is the spin pumping effect that has been recently proposed and observed in magnetic multilayers. The magnetization precession of a nanoscale ferromagnet in contact with a non-magnetic metallic media may transfer angular momentum to it. A spin current is then pumped into the non-magnetic conducting environment, profoundly affecting the ferromagnet magnetization dynamics. Spin pumping may also lead to a coupling of dynamic nature between magnetic units embedded in non-magnetic conducting matrices. Existing theories for the spin pumping effect are semi classic, and rely on the so called adiabatic approximation. In this thesis we develop a quantum and dynamic approach which allow us to calculate the spin current generated by the magnetization precession of a nanoscale ferromagnet in contact with a non-magnetic metallic media. We employ linear response theory to obtain an expression of the spin pumping current in terms of generalized transverse spin susceptibilities. To illustrate our theory and to explore the characteristics of the spin pumping currents we consider some very simple systems, consisting of a single moment attached to a non-magnetic linear chain. We compare our results with the existing theories, and discuss the advantages of our approach.