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Published on: October 19, 2015
Signatures of consolidated superparamagnetic and spin-glass behavior in magnetite-silver core-shell nanoparticles
Pinki Singh1, Manjari Shukla, Chandan Upadhyay
1School of Materials Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi, India-221005. psingh.rs.mst13@itbhu.ac.in cupadhyay.mst@iitbhu.ac.in.
Abstract:
A detailed investigation of magnetization relaxation for silver-coated magnetite nanostructures with three different types of magnetic behavior in a single particle is presented. Magnetite nanoparticles of diameter ∼6.5 nm synthesized via single-phase emulsion were further coated with a silver shell of thickness ∼2 nm. The synthesized nanoparticles are found to be efficiently photoluminescent. The coating of silver generates a magnetically disordered spin layer at the interface of the magnetic core and the non-magnetic shell. This intermediate layer plays a significant role in the dynamical magnetic response of nanoparticles under an external magnetic field. We present detailed magnetic measurements such as field- and temperature-dependent dc magnetization with zero-field-cooled and field-cooled protocols, ac susceptibility and time decay of magnetization relaxation along with their analysis using various formalisms viz. Néel-Arrhenius, Vogel-Fulcher and power law models. The relaxation analysis suggests the consolidated presence of two characteristic relaxation times corresponding to the superparamagnetic and spin-glass behavior of silver-coated magnetite nanoparticles.
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