Sub-3nm cobalt nanoparticles embedded in titania glass via ion implantation studied by polarised neutron reflectometry
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Date
2020-11-11
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Institute of Nuclear Science and Engineering (AINSE)
Abstract
Synthesis of stable metallic cobalt particles at the nanoscale is challenging using chemical methods due to their unstable nature and their tendency to oxidise. Nevertheless, ultra-small metallic cobalt nanoparticles offer unusual electronic and magnetic properties including large spin moments and magnetic anisotropy[1] [2]. Here we report the use of ion beam implantation to synthesis stable metallic cobalt nanoparticles embedded within TiO2-x thin films. Scanning transmission electron microscopy (STEM) images revealed that the Co nanoclusters were around 1-3 nm in size. The blocking temperature of Co nanoparticles is estimated to be TB = 6.5 K from the field-cooled and zero-field-cooled magnetization curves. Polarised neutron reflectometry (PNR) measurements reveal superparamagnetic behaviour with a strong temperature dependency due to the small size of the nanoclusters. The nuclear scattering length density, together with near-edge X-ray absorption spectroscopy (NEXAFS) show that the magnetic cobalt clusters are metallic and unoxidized below the TiO2-x surface, whereas near the surface the clusters are prone to form cobalt oxides in a magnetic dead layer that extends over a few nanometers. Our results show that ion beam synthesis can produce ultra-small particles that are not possible with other methods, and these particles survive for long periods without much oxidation.
Description
Keywords
Synthesis, Cobalt, Nanoparticles, Microscopy, Magnetization, Spectroscopy, Scattering, Anisotropy, Ions, Oxidation
Citation
Bake, A., Pastuovic, Z., Cortie, D., Mitchell, D., & Wang, X. (2020). Sub-3nm cobalt nanoparticles embedded in titania glass via ion implantation studied by polarised neutron reflectometry. Paper presented to the ANBUG-AINSE Neutron Scattering Symposium, AANSS 2020, Virtual Meeting, 11th - 13th November 2020. (pp. 43). Retrieved from: https://events01.synchrotron.org.au/event/125/attachments/725/1149/AANSS_Abstract_Booklet_Complete_-_1_Page_Reduced.pdf