Magnetism, magnetoresistance, and Shubnikov-de Haas oscillations in Na-implanted highly oriented pyrolitic graphite

• Autor(a) principal: Pires, Rafael Fernando
• Data de Publicação: 2012
• Outros Autores: Pureur Neto, Paulo, Behar, Moni, Pimentel Junior, Jorge Luiz, Schaf, Jacob, Kopelevich, Y.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da UFRGS
• Texto Completo: http://hdl.handle.net/10183/96545
• topic: Momentos magnéticos; Histerese magnética; Massa efetiva; Implantacao ionica; Distribuição de impurezas; Sódio; Grafite

We report on magnetization, magnetoresistance, and Shubnikov-de Haas oscillations experiments in Na-implanted samples of highly oriented pyrolitic graphite (HOPG). Different ion fluences were applied so that samples with Na contents of 0.5, 1.0, 1.5, and 2.0 at. % were obtained in the implanted region. Ferromagnetic-like hysteresis was observed in magnetization experiments where the field was applied parallel to the graphene planes. The observed saturation moment increases systematically as a function of the implanted ion concentration up to Na 1 at. %, where it goes through a maximum before decreasing slightly towards Na 2 at. %. The planar magnetoresistance amplitude at fixed field and temperature closely correlates with the saturation magnetization data. This result suggests that the strong planar magnetoresistance in graphite is at least partially related to a spin dependent mechanism. The magnetoresistance experiments also reveal the occurrence of Shubnikov-de Haas oscillations. The characteristic frequencies and the effective masses could be estimated and do not depend on the Na concentration. The reported experiments show that the expressive enhancement observed in ferromagnetic-like response in Na-implanted HOPG is primarily due to point defects produced by the implantation process.