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Morphology effects on exchange anisotropy in Co-CoO nanocomposite films
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2015 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 576, 11-18 p.Article in journal (Refereed) Published
Abstract [en]

Co-CoO composite films were prepared by solution chemical technique using amine-modified nitrates and acetates in methanol. We study how particle size and porosity can be tuned through the synthesis parameters and how this influences the magnetic properties. Phase content and microstructure were characterised with grazing incidence X-ray diffraction and electron microscopy, and the magnetic properties were studied by magnetometry and magnetic force microscopy. Composite films were obtained by heating spin-coated films in Ar followed by oxidation in air at room temperature, and the porosity and particle size of the films were controlled by gas flow and heating rate. The synthesis yielded dense films with a random distribution of metal and oxide nanoparticles, and layered films with porosity and sintered primary particles. Exchange anisotropy, revealed as a shift towards negative fields of the magnetic hysteresis curve, was found in all films. The films with a random distribution of metal and oxide nanoparticles displayed a significantly larger coercivity and exchange anisotropy field compared to the films with a layered structure, whereas the layered films displayed a larger nominal saturation magnetisation. The magnitude of the coercivity decreased with increasing Co grain size, whereas increased porosity caused an increased tilt of the magnetic hysteresis curve. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

Place, publisher, year, edition, pages
2015. Vol. 576, 11-18 p.
Keyword [en]
Co-CoO composite, Thin film, Solution chemical synthesis, Morphology effect, Magnetism, Exchange anisotropy, Magnetic stray field
National Category
Physical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
URN: urn:nbn:se:uu:diva-246807DOI: 10.1016/j.tsf.2014.11.064ISI: 000349373300002OAI: diva2:795552
Available from: 2015-03-16 Created: 2015-03-10 Last updated: 2016-06-01Bibliographically approved
In thesis
1. Solution-Chemical Synthesis of Cobalt and Iron:Zinc Oxide Nanocomposite Films
Open this publication in new window or tab >>Solution-Chemical Synthesis of Cobalt and Iron:Zinc Oxide Nanocomposite Films
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The potentially most important challenges today are related to energy and the environment. New materials and methods are needed in order to, in a sustainable way, convert and store energy, reduce pollution, and clean the air and water from contaminations. In this, nanomaterials and nanocomposites play a key role, and hence knowledge about the relation between synthesis, structure, and properties of nanosystems is paramount.

This thesis demonstrates that solution-chemical synthesis, using amine-modified acetates and nitrates, can be used to prepare widely different nanostructured films. By adjusting the synthesis parameters, metals, oxides, and metal–oxide or oxide–oxide nanocomposites were prepared for two systems based on Co and Zn:Fe, respectively, and the films were characterised using diffraction, spectroscopy, and microscopy techniques, and SQUID magnetometry.

A variety of crystalline cobalt films—Co metal, CoO, Co3O4, and composites with different metal:oxide ratios—were synthesised. Heat-treatment parameters and control of the film thickness enabled tuning of the phase ratios. Random and layered Co–CoO composites were prepared by utilising different heating rates and gas flow rates together with a morphology effect associated with the furnace tube. The Co–CoO films exhibited exchange bias due to the ferromagnetic–antiferromagnetic interaction between the Co and CoO, whereas variations in e.g. coercivity and exchange bias field were attributed to differences in the structure and phase distribution.

Ordered structures of wurtzite ZnO surrounded by amorphous ZnxFeyO were prepared through controlled phase segregation during the heating, which after multiple coating and heating cycles yielded ZnO–ZnxFeyO superlattices. The amorphous ZnxFeyO was a prerequisite for superlattice formation, and it profoundly affected the ZnO phase, inhibiting grain growth and texture, already from 1% Fe. In addition, ZnO–ZnxFeyO exhibited a photocatalytic activity for the oxidation of water that was higher than results reported for pure ZnO, and comparable to recent results reported for graphene-modified ZnO.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 85 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1356
Fe:Zn oxide, Co-CoO, Solution-chemical synthesis, Heat treatment parameters, Nanocomposite, Film, Multilayer, Phase ratio, Phase distribution, Exchange bias, Magnetism, Photocatalysis
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
urn:nbn:se:uu:diva-280619 (URN)978-91-554-9520-6 (ISBN)
Public defence
2016-06-09, Å 2005, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Available from: 2016-05-17 Created: 2016-03-11 Last updated: 2016-06-01

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