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Effects of the individual particle relaxation time on superspin glass dynamics
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Univ Castilla La Mancha, IRICA, E-13071 Ciudad Real, Spain.;Univ Castilla La Mancha, Dept Fis Aplicada, E-13071 Ciudad Real, Spain..
Inst Bioengn & Nanotechnol, 31 Biopolis Way, Singapore 138669, Singapore..
Univ Castilla La Mancha, IRICA, E-13071 Ciudad Real, Spain.;Univ Castilla La Mancha, Dept Fis Aplicada, E-13071 Ciudad Real, Spain..
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2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 5, 054407Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

The low temperature dynamic magnetic properties of two dense magnetic nanoparticle assemblies with similar superspin glass transition temperatures T-g similar to 140 K are compared. The two samples are made from batches of 6 and 8 nm monodisperse gamma-Fe2O3 nanoparticles, respectively. The properties of the individual particles are extracted from measurements on reference samples where the particles have been covered with a thick silica coating. The blocking temperatures of these dilute assemblies are found at 12.5 K for the 6 nm particles and at 35 K for the 8 nm particles, which implies different anisotropy energy barriers of the individual particles and vastly different temperature evolution of their relaxation times. The results of the measurements on the concentrated particle assemblies suggest a strong influence of the particle energy barrier on the details of the aging dynamics, memory behavior, and apparent superspin dimensionality of the particles.

Place, publisher, year, edition, pages
2016. Vol. 93, no 5, 054407
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-279564DOI: 10.1103/PhysRevB.93.054407ISI: 000369726000001OAI: oai:DiVA.org:uu-279564DiVA: diva2:908420
Funder
Swedish Research Council
Available from: 2016-03-02 Created: 2016-03-02 Last updated: 2017-04-07Bibliographically 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)
Opponent
Supervisors
Available from: 2017-05-10 Created: 2017-04-07 Last updated: 2017-05-16

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Andersson, Mikael SvanteNordblad, PerMathieu, Roland

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