Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis

Bake, A; Rezoanur Rahman, M; Evans, PJ; Cortie, M; Nancarrow, M; Abrudan, R; Radu, F; Khaydukov, Y; Causer, G; Callori, S; Livesey, KL; Mitchell, D; Pastuovic, Z; Wang, X; Cortie, D

Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis

Bake, A Rezoanur Rahman, M Evans, PJ Cortie, M

Nancarrow, M Abrudan, R Radu, F Khaydukov, Y Causer, G Callori, S Livesey, KL Mitchell, D Pastuovic, Z Wang, X Cortie, D

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Publisher:: Elsevier
Publication Type:: Journal Article
Citation:: Applied Surface Science, 2021, 570, pp. 1-13
Issue Date:: 2021-12-30

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Field	Value	Language
dc.contributor.author	Bake, A
dc.contributor.author	Rezoanur Rahman, M
dc.contributor.author	Evans, PJ
dc.contributor.author	Cortie, M https://orcid.org/0000-0003-3202-6398
dc.contributor.author	Nancarrow, M
dc.contributor.author	Abrudan, R
dc.contributor.author	Radu, F
dc.contributor.author	Khaydukov, Y
dc.contributor.author	Causer, G
dc.contributor.author	Callori, S
dc.contributor.author	Livesey, KL
dc.contributor.author	Mitchell, D
dc.contributor.author	Pastuovic, Z
dc.contributor.author	Wang, X
dc.contributor.author	Cortie, D
dc.date.accessioned	2022-02-04T03:11:33Z
dc.date.available	2022-02-04T03:11:33Z
dc.date.issued	2021-12-30
dc.identifier.citation	Applied Surface Science, 2021, 570, pp. 1-13
dc.identifier.issn	0169-4332
dc.identifier.issn	1873-5584
dc.identifier.uri	http://hdl.handle.net/10453/154186
dc.description.abstract	Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra-small, oxidation-resistant, cobalt nanoparticles embedded within substoichiometric TiO2-δ thin films. Using high fluence implantation of cobalt at 20–60 keV, the particles were assembled with an average size of 1.5 ± 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near-edge X-ray fluorescence spectroscopy on the L2,3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and superparamagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element-resolved X-ray magnetic circular dichroism, and depth-resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reactions.
dc.language	en
dc.publisher	Elsevier
dc.relation.ispartof	Applied Surface Science
dc.relation.isbasedon	10.1016/j.apsusc.2021.151068
dc.rights	info:eu-repo/semantics/closedAccess
dc.subject.classification	Applied Physics
dc.title	Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis
dc.type	Journal Article
utslib.citation.volume	570
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Science
pubs.organisational-group	/University of Technology Sydney/Faculty of Science/School of Mathematical and Physical Sciences
utslib.copyright.status	closed_access	*
pubs.consider-herdc	false
dc.date.updated	2022-02-04T03:11:29Z
pubs.publication-status	Published
pubs.volume	570

Abstract:

Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra-small, oxidation-resistant, cobalt nanoparticles embedded within substoichiometric TiO2-δ thin films. Using high fluence implantation of cobalt at 20–60 keV, the particles were assembled with an average size of 1.5 ± 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near-edge X-ray fluorescence spectroscopy on the L2,3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and superparamagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element-resolved X-ray magnetic circular dichroism, and depth-resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reactions.

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http://hdl.handle.net/10453/154186