Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8156140 | Journal of Magnetism and Magnetic Materials | 2015 | 8 Pages |
Abstract
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~2, 4.5, and 7Â nm, with narrow size distribution. transmission electron microscopy (TEM) images and X-ray diffraction (XRD) profiles indicates that samples with 7 and 4.5Â nm present a high crystallinity while the 2Â nm sample has a poor one. We have investigated by magnetization measurements and in-field Mössbauer spectroscopy the influence of the surface in the internal magnetic order of the particles. Particles with d=7Â nm have almost single domain behavior and the monodomain occupies approximately the whole particle. In the sample with d=4.5Â nm the surface anisotropy is large enough to alter the ferrimagnetic order in the particle shell. Then, a surface/volume ratio of ~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=2Â nm sample the poor crystallinity and the large surface/volume ratio avoid the ferrimagnetic order in the particle down to T=5Â K.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Condensed Matter Physics
Authors
Betiana N. Pianciola, Enio Jr., Horacio E. Troiani, Luiz C.C.M. Nagamine, R. Cohen, Roberto D. Zysler,