Structural and magnetic properties of core-shell Au/Fe3O4 nanoparticles

Abstract

We present a systematic study of core-shell Au/Fe3O4 nanoparticles 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 Fe3O4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe3O4 core-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 Fe3O4 shell) and spins located in the ordered region of the Fe3O4 shell.

Hydrothermal Synthesis of Nanooctahedra MnFe2O4 onto the Wood Surface with Soft Magnetism, Fire Resistance and Electromagnetic Wave Absorption

“…Figure 3b,c shows the Fe2p and the Mn2p spectra, respectively. For Fe, the two main peaks Fe2p 1/2 and Fe2p 3/2 at 724.73 eV and 711.13 eV, respectively, indicate the presence of Fe 3+ cations by comparison with the Fe2p 3/2 peaks of Fe 2 O 3 and Fe metal [30,31,32,33]. Two sharp peaks for the Mn2p 1/2 and Mn2p 3/2 at 653.23 eV and 641.43 eV, respectively, indicate the presence of Mn 2+ cations by comparison with the MnO [34].…”

Enhanced Exchange Bias Effect by Modulating Relative Ratio of Magnetic Ions in Y2Co2−xMnxO6 (x = 1.0–1.9)

“…It occurs typically in thin film bilayers, reflected in the unidirectional anisotropy of the AFM layer coupled with interfacial magnetic moments of the FM layer upon cooling to the Néel temperature in an applied magnetic field . Intensive studies of EB effect on core‐shell nanostructures have been conducted to find efficient means for nanoscale miniaturization of magnetic devices . Many efforts have been made to realize the EB effect on bulk ceramic materials by taking advantage of a simple synthesis procedure.…”

Iron Oxide and Gold Based Magneto-Plasmonic Nanostructures for Medical Applications: A Review

“…Felix et al [ 74 ] reported the preparation of spherical Au-Fe 3 O 4 core-shell NSs using thermal decomposition method. They mixed both ferric acetylacetonate and auric acetate salts in 1-octadecene and 1,2-hexadecanediol in presence of oleylamine and oleic acid surfactants.…”

“…Indeed, the interface region between the iron oxide and gold includes broken bonds, which may generate randomness and/or frustration in the exchange interaction between the outer magnetic cations and the inner ones [ 90 ]. In some cases, an exchange bias feature can be observed as illustrated in Figure 20 , with the appearance of a small shift, along the field axis, of the hysteresis loop recorded in FC conditions by comparison to that recorded in ZFC ones [ 74 ]. The iron oxide crystal size reduction leads also to surface iron cation spin disorder, which affects the total magnetic behaviour of the Fe 3− x O 4 matter, decreasing the whole magnetization and increasing the total anisotropy.…”

“…Recently, Felix et al [ 74 ] reported the structural and magnetic properties of AFNSs based on a 6.9 ± 1.0 nm in diameter Au core and a 3.5 nm in thickness Fe 3 O 4 shell. They observed that their hetero-nanostructures display a blocked state at temperatures lower than T B = 59 K and a superparamagnetic one at temperatures higher than T B .…”