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Exotic magnetism in ZnO based systems

Lundi 28 octobre 2013 10:30 - Duree : 1 heure
Lieu : Room 337, Central Building, ESRF - 6 Rue Jules Horowitz - Grenoble

Orateur : Clara GUGLIERI (Instituto de Ciencia de Materiales de Aragón (ICMA) - Spain)

We present a study of the local structure of ZnO capped nanoparticles and ZnO/ZnS multilayers, performed by using X-ray absorption spectroscopy (XAS), and X-ray Magnetic Circular Dichroism (XMCD) at the Zn, O and S K-edge. The experimental spectra have been compared to ab-initio calculations. ZnO nanoparticles (NPs) have been capped with three different organic molecules : tryoctylphosphine (TOPO), dodecylamine (AMINE), and dodecanethiol (THIOL), which bond to the particle surface through an O, N, and S atom respectively. Thin films were grown by RF sequential sputtering from ZnO and ZnS target. A combined element-specific XAS and XMCD study performed at the Zn K-edge demonstrates the occurrence of intrinsic ferromagnetic-like behaviour up to room temperature [1]. In addition, the analysis of XAS spectra of ZnO NPs capped with dodecanethiol points out the formation of a ZnO-ZnS core-shell structure and a ZnO-ZnS interface. Zn K-edge XMCD measurements reveal the coexistence of two different magnetic contributions : a paramagnetic response from the core-shell components of the NP, and a ferromagnetic contribution stemming from the interface. Our results indicate that ferromagnetism is favored in those regions of the interface where Zn-O bonds rather than Zn-S ones are involved [2,3]. We have extended these studies to the O K-edge, for which we have obtained a neat XMCD signal, and the S K-edge. The analysis of the XAS spectra fully support the conclusions derived from the analysis at the Zinc K-edge. Particularly, the comparison of the experimental spectra and the ab-initio calculations demonstrates the formation of the aforesaid ZnO-ZnS interface at both NPs capped with dodecanethiol and ZnO/ZnS multilayers. Accordingly, the ferromagnetic-like contribution is related to the structural details at this interface, where structural distortions play a fundamental role. [1] J. Chaboy et al, Phys. Rev. B 82, 064411 (2010). [2] C. Guglieri and J. Chaboy , J. Phys. Chem. C 114, 19629–19634 (2010) [3] C. Guglieri, M. A. Laguna-Marco, M. A. García, N. Carmona, E. Céspedes, M. García-Hernández, A. Espinosa, J. Chaboy, J. Phys. Chem. C 116, 6608−6614 (2012)

Contact : eva.jahn@esrf.freva.jahn@esrf.fr

Discipline évènement : (Physique)
Entité organisatrice : (ESRF)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire ESRF)
Site de l'évènement : Polygone scientifique

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