# Spin-glass freezing of maghemite nanoparticles prepared by microwave plasma synthesis

Nadeem, K.; Krenn, H.; Traussnig, T.; Würschum, R.; Szabo, D.V.; Letofsky-Papst, I.

##### Abstract:
Magnetic properties of 6nm maghemite nanoparticles (prepared by microwave plasma synthesis) have been studied by ac and dc magnetic measurements. Structural characterization includes x-ray diffraction and transmission electron microscopy. The temperature scans of zero field cooled/field cooled (ZFC/FC) magnetization measurements show a maximum at 75 K. The ZFC/FC data are fitted to the Brown-Ne´el relaxation model using uniaxial anisotropy and a log-normal size-distribution function to figure out the effective anisotropy constant K$_{eff}$. K$_{eff}$ turns out to be larger than the anisotropy constant of bulk maghemite. Fitting of the ac susceptibility to an activated relaxation process according to the Arrhenius law provides unphysical values of the spin-flip time and activation energy. A power-law scaling shows a satisfactory fit to the ac susceptibility data and the dynamic critical exponent (zv$\thickapprox$10) takes value between 4 and 12 which is typical for the spin-glass systems. The temperature dependence of coercivity and exchange bias shows a sharp increase toward low temperatures which is due to enhanced surface anisotropy. ... mehr

 Zugehörige Institution(en) am KIT Institut für Angewandte Materialien - Werkstoffprozesstechnik (IAM-WPT) Publikationstyp Zeitschriftenaufsatz Jahr 2012 Sprache Englisch Identifikator ISSN: 0021-8979, 0148-6349, 1089-7550, 1520-8850, 2163-5102 urn:nbn:de:swb:90-AAA1100870102 KITopen-ID: 110087010 HGF-Programm 43.12.01 (POF II, LK 01) Erschienen in Journal of applied physics Band 111 Seiten Art.Nr. 113911/1-6 Nachgewiesen in ScopusWeb of Science
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