Dinâmica de spins na presença de defeitos em estruturas magnéticas confinadas: aplicações a nanodiscos magnéticos

• Autor(a) principal: Silva, Ricardo Lopes da
• Data de Publicação: 2009
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/952
• topic: Nanomagnetismo; Vórtices; Dinâmica de spins; Nanomagnetism; Vortex; Spin dynamics; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA::FISICA DA MATERIA CONDENSADA

In this work we investigate the influence of artificial defects inserted into thin magnetic nanodisks on the vortex core dynamics. First we consider the presence of one and two holes (antidots). In general, the core falls into the hole but, in particular, we would like to remark an interesting phenomenon not yet observed, which is the vortex core switching induced by the vortex-hole interactions. It occurs for the case with only one hole and for very special conditions involving the hole size and position as well as the disk size. Any small deformation in the disk geometry such as the presence of a second antidot changes completely the vortex dynamics and the vortex core eventually falls into one of the defects. After trapped, the vortex center still oscillates with a very high frequency and small amplitude around the defect center. It is important to remark that these kinds of defects can be already artificially produced in magnetic nanodisks by lithographic techniques. We also study the effects of another type of defect (a line defect) on the vortex. It is done by studying a nanodisk possessing two coupled materials with different ferromagnetic exchange constant. The common border line of the two media passes at the disk center dividing the system exactly in two similar semidisks. The main result of this study is that, depending on the magnetic coupling which connects the media, the vortex core can be dramatically and repeatedly flipped from up to down and vice versa by the interface. This amazing phenomenon is source of a burstlike emission of spin waves each time the switching process takes place. To our knowledge, such a nanodisk with an interface was not realized in laboratories yet. The vortex core motion was investigated with a simple description based on a two- dimensional odel which mimics a very thin real material with defects.