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Ageing dynamics of a superspin glass
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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2014 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 108, no 1, 17004- p.Article in journal (Refereed) Published
Abstract [en]

Magnetization dynamics of a model superspin glass system consisting of nearly monodispersed close-packed maghemite particles of diameter 8 nm is investigated. The observed non-equilibrium features of the dynamics are qualitatively similar to those of atomic spin glass systems. The intrinsic relaxation function, as observed in zero-field-cooled magnetization relaxation experiments, depends on the time the sample has been kept at constant temperature (ageing). Accompanying low-field experiments show that the archetypal spin glass characteristics -ageing, memory and rejuvenation- are reproduced in this dense system of dipolar-dipolar interacting superspins.  

Place, publisher, year, edition, pages
2014. Vol. 108, no 1, 17004- p.
National Category
Materials Engineering Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-238588DOI: 10.1209/0295-5075/108/17004ISI: 000343970300018OAI: oai:DiVA.org:uu-238588DiVA: diva2:772183
Available from: 2014-12-16 Created: 2014-12-14 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Interacting Magnetic Nanosystems: An Experimental Study Of Superspin Glasses
Open this publication in new window or tab >>Interacting Magnetic Nanosystems: An Experimental Study Of Superspin Glasses
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents experimental results on strongly interacting γ-Fe2O3 magnetic nanoparticles and their collective properties. The main findings are that very dense randomly packed (≈60%) γ-Fe2O3 nanoparticles form a replica of a spin glass. The magnetic properties of the nanoparticle system are in most regards the same as those of an atomic spin glass. The system is therefore proposed as a model superspin glass. In superspin glasses the interacting building blocks that form the collective state are single domain nanoparticles, superspins with a magnetic moment of about 10000 μB, which can be compared to the atomic magnetic moment in spin glasses of approximately 1 μB.  It was found that the relaxation time of the individual nanoparticles impacts the collective properties and governs the superspin dimensionality. Several dense compacts, each prepared with nanoparticles of a specific size, with diameters 6, 8, 9 and 11.5 nm, were studied. All the studied compacts were found to form a superspin glass state. Non-interacting reference samples, consisting of the same particles but coated with a silica shell, were synthesized to determine the single particle magnetic properties.  It was also found that the effects of the nanoparticle size distribution, which lead to a variation of the magnetic properties, can be mitigated by having strong enough interparticle interactions. The majority of the work was carried out using SQUID magnetometry.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1505
Keyword
spin glass, SQUID magnetometry, maghemite, magnetism, nanoparticles
National Category
Engineering and Technology Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-319717 (URN)978-91-554-9893-1 (ISBN)
Public defence
2017-06-02, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Supervisors
Available from: 2017-05-10 Created: 2017-04-07 Last updated: 2017-05-16

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Andersson, Mikael SvanteMathieu, RolandNordblad, Per

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