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Register a new userMorphology and magnetic properties of Fe3O4-alginic acid nanocomposites
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Added by
Bartlomiej Andrzejewski
Publication date
2013
fields
Physics
and research's language is
English
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Morphology, structure and magnetic properties of nanocomposites of magnetite (Fe3O4) nanoparticles and alginic acid (AA) are studied. Magnetite Fe3O4 nanoparticles and the nanoparticles capped with alginic acid exhibit very distinct properties. The chemical bonding between alginic acid and surface of magnetite nanoparticles results in recovery of surface magnetization. On the other hand, it also leads to enhanced surface spin disorder and unconventional behavior of magnetization observed in Fe3O4-AA nanocomposites at low temperatures.
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We report exchange bias (EB) effect in the Au-Fe3O4 composite nanoparticle system, where one or more Fe3O4 nanoparticles are attached to an Au seed particle forming dimer and cluster morphologies, with the clusters showing much stronger EB in comparison with the dimers. The EB effect develops due to the presence of stress in the Au-Fe3O4 interface which leads to the generation of highly disordered, anisotropic surface spins in the Fe3O4 particle. The EB effect is lost with the removal of the interfacial stress. Our atomistic Monte-Carlo studies are in excellent agreement with the experimental results. These results show a new path towards tuning EB in nanostructures, namely controllably creating interfacial stress, and open up the possibility of tuning the anisotropic properties of biocompatible nanoparticles via a controllable exchange coupling mechanism.
We report on the effect of organic acid capping on the behavior of magnetite nanoparticles. The nanoparticles of magnetite were obtained using microwave activated process, and the magnetic properties as well as the electron magnetic resonance behavior were studied for the Fe3O4 nanoparticles capped with alginic acid. The capped nanoparticles exhibit improved crystalline structure of the surface which leads to an enhanced magnetization. The saturation magnetization Ms increases to ~75% of the bulk magnetization. The improved structure also facilitates quantization of spin-wave spectrum in the finite size nanoparticles and this in turn is responsible for unconventional behavior at low temperatures. In magnetic resonance these anomalies are manifested as an unusual increase in the resonant field Hr(T) and also as a maximum of the spectroscopic splitting geff parameter at low temperatures. The unconventional behavior of the nanoparticles also leads to pronounced upturn of magnetization at low temperatures and a deviation from the Bloch law M(T) T^3/2.
We present a systematic study of core-shell Au/Fe_3O_4 nanoparticles produced by thermal decomposition under mild conditions. The morphology and crystal structure of the nanoparticles revealed the presence of Au core of <d> = (6.9pm 1.0) nm surrounded by Fe_3O_4 shell with a thickness of ~3.5 nm, epitaxially grown onto the Au core surface. The Au/Fe_3O_4 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 T_B = 59 K and a relaxed state well above T_B. 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 (H_{EX}) 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 Fe_3O_4 shell) and spins located in the ordered region of the Fe_3O_4 shell.
Atomic Force Microscopy and Grazing incidence X-ray diffraction measurements have revealed the presence of ripples aligned along the $[1bar{1}0]$ direction on the surface of (Ga,Mn)As layers grown on GaAs(001) substrates and buffer layers, with periodicity of about 50 nm in all samples that have been studied. These samples show the strong symmetry breaking uniaxial magnetic anisotropy normally observed in such materials. We observe a clear correlation between the amplitude of the surface ripples and the strength of the uniaxial magnetic anisotropy component suggesting that these ripples might be the source of such anisotropy.
Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe3O4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by x-ray photo electron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach x-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34nm) while the Fe3O4 films relax continuously up to the thickness of 50nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe3O4-NiO interface roughens continuously up to 1nm root-mean-square roughness with increasing NiO film thickness while the Fe3O4 surface is very smooth independent on the Fe3O4 film thickness. Finally, the Fe3O4-NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO-MgO interface is expanded.
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