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Title: Superparamagnetic relaxation and magnetic anisotropy energy distribution in CoFe{sub 2}O{sub 4} spinel ferrite nanocrystallites

Abstract

Superparamagnetism is a unique feature of magnetic nanoparticles. Spinel ferrite nanoparticles provide great opportunities for studying the mechanism of superparamagnetic properties. CoFe{sub 2}O{sub 4} nanocrystallites have been synthesized with a microemulsion method. The neutron diffraction studies and the temperature-dependent decay of magnetization show the superparamagnetic relaxation occurring in these nanoparticles. The neutron diffraction shows a high degree of inversion with the 78% tetrahedral sites occupied by Fe{sup 3+} cations. The nanoparticles with a 12 nm diameter have a blocking temperature around 320 K. The field-cooled and zero-field-cooled magnetization measurements display a divergence below the blocking temperature. The energy barrier distribution of magnetic anisotropy is derived from the temperature-dependent decay of magnetization. The magnetic anisotropy is clearly the origin of the divergence in the field-cooled and zero-field-cooled magnetization measurements. The energy barrier distribution function is used in a computer simulation of the zero-field-cooled magnetization, and the calculated magnetization has a great consistency with experimentally measured values. These studies on the magnetic anisotropy distribution elucidate the mechanism of superparamagnetic relaxation and facilitate the design and control of superparamagnetic properties in nanoparticles.

Authors:
; ;  [1]
  1. Georgia Inst. of Tech., Atlanta, GA (United States). School of Chemistry and Biochemistry
Publication Date:
Sponsoring Org.:
Office of Naval Research, Washington, DC (United States); USDOE, Washington, DC (United States)
OSTI Identifier:
691303
DOE Contract Number:  
AC05-96OR22464
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 103; Journal Issue: 33; Other Information: PBD: 19 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; SUPERPARAMAGNETISM; ANISOTROPY; RELAXATION; ENERGY SPECTRA; SPINELS; COBALT OXIDES; IRON OXIDES

Citation Formats

Rondinone, A.J., Samia, A.C.S., and Zhang, Z.J. Superparamagnetic relaxation and magnetic anisotropy energy distribution in CoFe{sub 2}O{sub 4} spinel ferrite nanocrystallites. United States: N. p., 1999. Web. doi:10.1021/jp9912307.
Rondinone, A.J., Samia, A.C.S., & Zhang, Z.J. Superparamagnetic relaxation and magnetic anisotropy energy distribution in CoFe{sub 2}O{sub 4} spinel ferrite nanocrystallites. United States. doi:10.1021/jp9912307.
Rondinone, A.J., Samia, A.C.S., and Zhang, Z.J. Thu . "Superparamagnetic relaxation and magnetic anisotropy energy distribution in CoFe{sub 2}O{sub 4} spinel ferrite nanocrystallites". United States. doi:10.1021/jp9912307.
@article{osti_691303,
title = {Superparamagnetic relaxation and magnetic anisotropy energy distribution in CoFe{sub 2}O{sub 4} spinel ferrite nanocrystallites},
author = {Rondinone, A.J. and Samia, A.C.S. and Zhang, Z.J.},
abstractNote = {Superparamagnetism is a unique feature of magnetic nanoparticles. Spinel ferrite nanoparticles provide great opportunities for studying the mechanism of superparamagnetic properties. CoFe{sub 2}O{sub 4} nanocrystallites have been synthesized with a microemulsion method. The neutron diffraction studies and the temperature-dependent decay of magnetization show the superparamagnetic relaxation occurring in these nanoparticles. The neutron diffraction shows a high degree of inversion with the 78% tetrahedral sites occupied by Fe{sup 3+} cations. The nanoparticles with a 12 nm diameter have a blocking temperature around 320 K. The field-cooled and zero-field-cooled magnetization measurements display a divergence below the blocking temperature. The energy barrier distribution of magnetic anisotropy is derived from the temperature-dependent decay of magnetization. The magnetic anisotropy is clearly the origin of the divergence in the field-cooled and zero-field-cooled magnetization measurements. The energy barrier distribution function is used in a computer simulation of the zero-field-cooled magnetization, and the calculated magnetization has a great consistency with experimentally measured values. These studies on the magnetic anisotropy distribution elucidate the mechanism of superparamagnetic relaxation and facilitate the design and control of superparamagnetic properties in nanoparticles.},
doi = {10.1021/jp9912307},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
number = 33,
volume = 103,
place = {United States},
year = {1999},
month = {8}
}