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Superspin glass behavior of self-interacting CoFe2O4 nanoparticles

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Title Superspin glass behavior of self-interacting CoFe2O4 nanoparticles
 
Creator MOHAPATRA, J
MITRA, A
BAHADUR, D
ASLAM, M
 
Subject SURFACE SPIN DISORDER
VOGEL-FULCHER LAW
MAGNETIC-RELAXATION
DYNAMICS
SYSTEMS
CO
Cobalt ferrite
Nanoparticles
Superparamagnetic
Superspin glass
 
Description Low-temperature magnetic properties of CoFe2O4 nanoparticles (3-16 nm) have been investigated by AC and DC magnetic measurements. The saturation magnetization (M-S) of ultra-small CoFe2O4 nanoparticles (3-9 nm) sharply increases at low temperature (10 K) compared to room temperature (RT) MS value. For example, the increment in M-S value for 3 nm CoFe2O4 nanoparticle is 22 emu/g and is null for 12 nm and larger sized nanoparticles. A similar trend of increment in MS is also seen in ultra-small size Fe3O4 and MnFe2O4 nanoparticles. However, the M-S enhancement in ultra-small CoFe2O4 nanoparticles is found much higher as compared to Fe3O4 and MnFe2O4 nanoparticles. The ultra-small sized nanoparticles arrange with a high packing density to induce a strong exchange as well as dipolar interactions, which renders the enhanced low temperature M-S with superspin glass (SSG) state. The exchange coupling strongly depends on magnetic anisotropy energy, which increases in the order Mn2+ < Fe2+ < Co2+ and thus the ultra-small CoFe2O4 nanoparticles show a large enhancement of M-S at low temperature due to strong exchange coupling. A noticeable enhancement of spin glass temperature (T-g) for ultra-small sized CoFe2O4 nanoparticles also confirms the presence of strong exchange coupling in this case. Fitting of the ac susceptibility chi'(T, f) data to a power-law scaling and Vogel-Fulcher model shows a satisfactory fit and the dynamic critical exponent takes value between 8.9 and 11.9 which are in a range typical for the spin-glass systems. Memory behavior in ultra-small CoFe2O4 nanoparticles suggest that the frequency dependent blocking process of ultra-small sized nanoparticles can be better described by power law model, while the interaction regime present in the 12 nm and above sized nanoparticles is ascribed to a Vogel-Fulcher model. (C) 2015 Elsevier B.V. All rights reserved.
 
Publisher ELSEVIER SCIENCE SA
 
Date 2016-01-14T14:13:10Z
2016-01-14T14:13:10Z
2015
 
Type Article
 
Identifier JOURNAL OF ALLOYS AND COMPOUNDS, 628,416-423
0925-8388
1873-4669
http://dx.doi.org/10.1016/j.jallcom.2014.12.197
http://dspace.library.iitb.ac.in/jspui/handle/100/17698
 
Language en