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Surface Spin-glass Freezing and Blocking in NiFe2O4 Nanoparticles

Published online by Cambridge University Press:  01 February 2011

Kashif Nadeem  and
Heinz Krenn
Kashif Nadeem
Affiliation:
kashif.nadeem@edu.uni-graz.at, Karl-Franzens university, Institute for Physics, Graz, Austria
Heinz Krenn
Affiliation:
heinz.krenn@uni-graz.at, Karl-Franzens university, Institute for Physics, Graz, Steiermark, Austria
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Abstract

We prepared single-phase nickel ferrite nanoparticles separated by silicon dioxide using sol-gel method with tetraethyl orthosilicate (TEOS) as a precursor for SiO2. The magnetic properties are investigated by using SQUID-magnetometry over a broad temperature range (4.2 – 350 K), magnetic field (2–70,000 Oe) and frequency (0.1 – 1000 Hz) range. The particle size is in the range 8 – 12 nm. Exchange bias and spin disorder appear at the core-shell interface due to broken bonds on the surface. Disorder and core-shell interaction induces spin-glass freezing which is manifested by a low temperature peak in the AC susceptibility well separated from magnetic blocking peak. This low temperature peak is assigned to spin-glass freezing. The proof of spin-glass freezing is managed by zero field cooled/field cooled (ZFC/FC), frequency and DC field dependence of AC susceptibility, low temperature hysteresis loop and time dependent thermoremanent magnetization at different temperatures. All the measurements stated above signify blocking/unblocking at higher temperatures and surface spin-glass freezing at low temperatures. The aim of our work is to contribute to a better understanding of “spin-frozen” magnetic ferrite nanoparticles at diameters 8 – 12 nm which could be important in future for stabilizing the magnetic state of “core-shell”-structured nanomagnets.

Keywords

magnetic propertiescore/shellnanoscale
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1256: Symposium N – Functional Oxide Nanostructures and Heterostructures , 2010 , 1256-N06-06
Copyright
Copyright © Materials Research Society 2010

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