Structural and magnetic properties of core-shell Au/Fe3O4nanoparticles.
We present a systematic study of core-shell Au/Fe3O4nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of d = (6.9 ± 1.0) nm surrounded by Fe3O4shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4core-shell structure was demonstrated by high angle annular dark field scanning transmission electron microscopy analysis. The magnetite shell grown on top of the Au nanoparticle displayed a thermal blocking state at temperatures below TB= 59 K and a relaxed state well above TB. Remarkably, an exchange bias effect was observed when cooling down the samples below room temperature under an external magnetic field. Moreover, the exchange bias field (HEX) started to appear at T~40 K and its value increased by decreasing the temperature. This effect has been assigned to the interaction of spins located in the magnetically disordered regions (in the inner and outer surface of the Fe3O4shell) and spins located in the ordered region of the Fe3O4shell.
Laboratory of Magnetic Characterization, Instituto de Física, Universidade de Brasília, DF 70910-900, Brasília, Brazil.|Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain.
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León Félix
Laboratory of Magnetic Characterization, Instituto de Física, Universidade de Brasília, DF 70910-900, Brasília, Brazil.
J A H
JA
Coaquira
Laboratory of Magnetic Characterization, Instituto de Física, Universidade de Brasília, DF 70910-900, Brasília, Brazil.
M A R
MA
Martínez
Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain.
G F
GF
Goya
Laboratory of Magnetic Characterization, Instituto de Física, Universidade de Brasília, DF 70910-900, Brasília, Brazil.
J
J
Mantilla
Green Nanotechnology Group, Faculdade de Ceilândia, Universidade de Brasília, Ceilândia, DF 72220-900, Brasília, Brazil.
M H
MH
Sousa
Cavendish Laboratory, Department of Physics, University of Cambridge, J.J Thomson Av., Cambridge CB3 0HE, United Kingdom.
L de Los Santos
LL
Valladares
Cavendish Laboratory, Department of Physics, University of Cambridge, J.J Thomson Av., Cambridge CB3 0HE, United Kingdom.
C H W
CH
Barnes
Laboratory of Magnetic Characterization, Instituto de Física, Universidade de Brasília, DF 70910-900, Brasília, Brazil.|School of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China.
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PC
Morais