Preparation And Properties Study Of Superparamagnetic Iron Oxide And LSMO/BCFO Multiferroic Thin Film

Superparamagnetic iron oxide (SPIO) nanoparticles show superparamagnetism and good stability, which make them the best candidate for the widely used as a magnetic resonance imaging (MRI) contrast agent. MRI is a powerful clinical diagnostic modality for the detection and diagnosis of a wide varity of diseases. MRI contrast agent is a diagnostic agent that could be administered to a patient in order to shorten the relaxation times of protons in tissues in which the agent accumulates, enhancing the imaging contrast between normal and diseased tissue. In this thesis, as the SPIO is core, the dextran is dispersant, we synthezise the dextran-coated SPIO nanoparticles by coprecipitation technique at first; under the catalysis of epichlorohydrin, the ethylenediamine was added, the hydroxyl on the surface of dextran is replaced by the amino-group, finally amino-group functionalized SPIO (SPIO-NH2) was obtained. In preparation process, we focus on the functionalization of SPIO with amino-group, and optimize the preparation technology, in which the amount of surface amino-group of the SPIO-NH2 nanoparticles is highest. The structure and magnetism of these SPIO-NH2 nanoparticles were also studied, it found that SPIO-NH2 nanoparticles possess superparamagnetic behavior. In a 1.5 T MR system, SPIO-NH2 nanoparticles can shorten the T2 signal relaxation time of liver tissue dramatically. Furthermore, Tat (FITC) peptide was choosen to conjugated with SPIO-NH2 nanoparticles, we obtain the magnetic/fluorescent bifunctional labeling prode; The obtained probe not only can enter the neural stem cells for cells labeling, but also result in significant negative T2 signal contrast enhancement, and can be used for magnetically labeling in a MR system.In a certain temperature range, multiferroics shows coexistent ferroelectric order and magnetic order, the coexistent ferroelectricity and magnetism can couple with each other and result in magneto-electric effects, so the multiferroics was considered to have important potential application in the semi-conductor devices, such as sensors, switches and modulators et al. In recent years, much attention were paid on multiferroics, which can be divided into single-phase multiferroics and composite multiferroics. The composite multiferroics prior to single-phase counterpart since they can produce stronger magneto-electric effects, which makes them possess widely application value, and also evokes more and more attention. In this thesis, single-phase ferromagnetic material and single-phase ferroelectric material were adopted to prepare multiferroic composite thin films. La0.67Sr0.33MnO3 (LSMO) is a typical ferromagnetic material with perovskite structure; while BiFeO3 (BFO) is also a perovskite typed multiferroics, which ferroelectric-paraelectric transition Curie temperature is Tc= 1103 K and its antiferromagnetic-paramagnetic transition Neel temperature is TN= 643 K, so BFO shows coexistent ferroelectricity and weak magnetism at room temperature. Based on the above, the ferromagnetic material LSMO (at room temperature) and the ferroelectric material BFO (at room temperature) were choosen to fabricate LSMO (7 layers)/BFO multiferroic composite thin films with different BFO layers by sol-gel technique, and further focus on its structure, morphology, ferroelectricity, dielectric properties et al, we found that the ferroelectricity of LSMO/BFO multiferroic thin films is enhanced when compared with that of BFO films. In addition, A site Ca substituted Bi1-xCaxFeO3 (BCFO) single-phase thin films was prepared by adding Ca(NO3)2*4H2O as starting material, and LSMO/BCFO multiferroic thin films was also obtained; the structure, morphology, ferroelectricity, dielectric properties et al of BCFO thin films and LSMO/BCFO composite thin films were also analysed. The results show that the doping of Ca can dramatically enhance the ferroelectricity of BCFO multiferroic thin films, which arises from the structure evolution of BFO. In addition, the remnant polarization and saturated polarization of LSMO/BCFO thin films are higher than that of pure BCFO thin films, shows enhanced ferroelectricity in LSMO/BCFO thin films, which originate from the magneto-electric coupled effects between LSMO layer and BCFO layer.