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Memory and superposition in a spin glass
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science.
2001 In: Phys. Rev. B, Vol. 63, 092401- p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2001. Vol. 63, 092401- p.
URN: urn:nbn:se:uu:diva-89864OAI: oai:DiVA.org:uu-89864DiVA: diva2:161687
Available from: 2002-05-13 Created: 2002-05-13 Last updated: 2013-03-21
In thesis
1. Anisotropy, disorder and frustration in magnetic nanoparticle systems and spin glasses
Open this publication in new window or tab >>Anisotropy, disorder and frustration in magnetic nanoparticle systems and spin glasses
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetic properties of nanoparticle systems and spin glasses have been investigated theoretically, and experimentally by squid magnetometry.

Two model three-dimensional spin glasses have been studied: a long-range Ag(11 at% Mn) Heisenberg spin glass and a short-range Fe0.5Mn0.5TiO3 Ising spin glass. Experimental protocols revealing ageing, memory and rejuvenation phenomena are used. Quantitative analyses of the glassy dynamics within the droplet model give evidences of significantly different exponents describing the nonequilibrium dynamics of the two samples. In particular, non-accumulative ageing related to temperature-chaos is much stronger in Ag(11 at% Mn) than in Fe0.5Mn0.5TiO3.

The physical properties of magnetic nanoparticles have been investigated with focus on the influence of dipolar interparticle interaction. For weakly coupled nanoparticles, thermodynamic perturbation theory is employed to derive analytical expressions for the linear equilibrium susceptibility, the zero-field specific heat and averages of the local dipolar fields. By introducing the averages of the dipolar fields in an expression for the relaxation rate of a single particle, a non trivial dependence of the superparamagnetic blocking on the damping coefficient is evidenced. This damping dependence is interpreted in terms of the nonaxially symmetric potential created by the transverse component of the dipolar field.

Strongly interacting nanoparticle systems are investigated experimentally in terms of spin-glass behaviour. Disorder and frustration arise in samples consisting of frozen ferrofluids from the randomness in particle position and anisotropy axes orientation. A strongly interacting system is shown to exhibit critical dynamics characteristic of a spin-glass phase transition. Ageing, memory and rejuvenation phenomena similar to those of conventional spin glasses are observed, albeit with weak temperature-chaos effects.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2002. 71 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 727
Materials science, Materialvetenskap
National Category
Materials Engineering
Research subject
Solid State Physics
urn:nbn:se:uu:diva-2038 (URN)91-554-5344-9 (ISBN)
Public defence
2002-06-04, Polhemssalen at the Ångström Laboratory, Uppsala, 10:15
Available from: 2002-05-13 Created: 2002-05-13Bibliographically approved

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