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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Size and surface effects in the magnetic order of CoFe2O4 nanoparticles

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Pianciola, Betiana N. [1, 2] ; Lima, Jr., Enio [2] ; Troiani, Horacio E. [1, 2] ; Nagamine, Luiz C. C. M. [3] ; Cohen, R. [3] ; Zysler, Roberto D. [1, 2]
Total Authors: 6
[1] Inst Balseiro SC, RA-8400 San Carlos De Bariloche, Rio Negro - Argentina
[2] CONICET SC, CNEA, Ctr Atom Bariloche, RA-8400 San Carlos De Bariloche, Rio Negro - Argentina
[3] Univ Sao Paulo, Inst Fis, BR-05508090 Sao Paulo - Brazil
Total Affiliations: 3
Document type: Journal article
Source: Journal of Magnetism and Magnetic Materials; v. 377, p. 44-51, MAR 1 2015.
Web of Science Citations: 17

In this work, we have focused on the size dependence of the magnetic properties and the surface effects of CoFe2O4 nanoparticles synthesized by high temperature chemical method with diameter d similar to 2, 4.5, and 7 nm, with narrow size distribution, transmission electron microscopy (TEM) images and X-ray diffraction (XRD) profiles indicates that samples with 7 and 4.5 nm present a high crystallinity while the 2 nm sample has a poor one. We have investigated by magnetization measurements and in held Mossbauer spectroscopy the influence of the surface in the internal magnetic order of the particles. Particles with d=7 nm have almost single domain behavior and the monodomain occupies approximately the whole particle. In the sample with d=4.5 nm the surface anisotropy is large enough to alter the ferrimagnetic order in the particle shell. Then, a surface/volume ratio of similar to 60% is the crossover between a single domain nanoparticle and a frustrated order in a magnetic core -shell structure, due to the competition between surface anisotropy and exchange interaction + crystalline anisotropy in cobalt ferrite. In the d=2 nm sample the poor crystallinity and the large surface/volume ratio avoid the ferrimagnetic order in the particle down to T=5 K. (C) 2014 Elsevier B.V. All rights reserved. (AU)