Full text
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| Author(s): |
José Jadsom Sampaio de Figueiredo
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2008-07-11 |
| Examining board members: |
Abner de Siervo;
Colin Clark;
Francis Claudon;
Jonder Morais;
Varlei Rodrigues
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| Advisor: | Abner de Siervo; Flávio Garcia |
| Abstract | |
Metallic Nanoparticles (NP's), ultra-thin films and nano-structured systems have motivated several theoretical and experimental works because of their new electronic optical and magnetic properties of these materials. In NP's, such properties are directly related to the size and surface effects, which affect its electronic and crystallographic structures, by concentrating a larger number of atoms on the surface in relation to their volume. Recent studies have suggested that some noble metals without any kind of spontaneous ferromagnetic order can exhibit it, even at room temperature, when segmented as nanoparticles. Examples of these metals are Au and Pd. Despite the efforts to prove the existence of a ferromagnetic behavior in such materials, there are no measurements that demonstrate unambiguously the ferromagnetic polarization in Pd atoms, for example. Most of the works shown in the literature have used SQUID measurements to characterize the ferromagnetism in these materials. It is therefore necessary to verify the existence of ferromagnetism in these materials by using element specific techniques, such as XMCD (X-ray magnetic circular dichroism). XMCD is a very important technique, which is element selective and performs quantitative determination of the spin and orbital magnetic contributions for each element separately. Our work has a particular difference when compared to others in literature because instead of studying each element individually we have worked with NP's of the bimetallic compound Aux Pd1-x (x = 0.00, 0.25, 0.50, 0.75) capped by thiol. SQUID measurements clearly showed ferromagnetic behavior in these nanoparticles, even at room temperature. In this thesis we will present results of a systematic characterization of these nanoparticles by a multi-technique approach which involves measurements with SQUID, XANES, XPS and XMCD in the L2,3 edges of the Pd and Au L3 edge. We also emphasize the development of a new instrumentation for XMCD measurements at UHV where samples can be submitted to high magnetic fields and conditions of low temperatures. Based on these findings we discuss the possibility of ferromagnetism in these nanoparticles and its origin (AU) | |
| FAPESP's process: | 06/05357-0 - Study of magnetic properties of Pd nanoparticles and utrathin films |
| Grantee: | José Jadsom Sampaio de Figueiredo |
| Support Opportunities: | Scholarships in Brazil - Master |