Ordered Magnetic Nanocomposites: Synthesis And Magnetic Properties

The magnetic properties of nanocomposites not only depended on the intrinsic magnetic properties of the nanoparticles,but also were affected by the magnetic exchange interactions between nanoparticles.The distribution of the size,shape,defects and phase purity greatly affected the magnetic properties of nanocomposites,which made the investigation of magnetism and exchange interactions of nanocomposites very complex.Homogeneous component and controllable morphology were the essential condition of the synthesis of the magnetic nanocomposites,and these special magnetic nanocomposites would lay the foundations of developing practical applications of spintronic devices and ultrahigh density media.In this paper,mesoporous monophase nanowires were synthesized used the ordered mesoporous silica SBA-15 as template by the nanocasting route.We obtained the different morphology nanowires through changing the preparation condition and discussed the magnetic properties of the nanowires.Furthermore,we synthesized the magnetic nanocomposites used the ordered nanowires via a n impregnation method,and then we discussed the magnetic properties of the magnetic nanocomposites.Firstly,mesoporous SBA-15 were synthesis with block polymer as a template and TEOS as a silica source by the hydrothermal method.We obtained mesoporous SBA-15 with the ordered hexagonal straight channel structure.Secondly,Co₃O₄ and CoFe₂O₄ nanowires with different morphology?dispersed and bundled?were synthesized used the ordered mesoporous silica SBA-15 as template by the technique of concentration and nanocasting method.It was found that the dispersed nnaowires were only composed of several nanowires,while the bundled nanowires consisted of tens of nanowires,the Co₃O₄ and the CoFe₂O₄ nanowire arrays presented the similar ordered structures to SBA-15,indicating the change trend of microstructure to the bulk Co₃O₄.The two morphology nanowires had a big difference in magnetic property.With the smaller interwires distance?2 nm?of mesoporous Co₃O₄ nanowires,the surface spin at the neighboring nanowires coupled each other.As the result,M of bundled nanowires?3.39emu/g?was lower than that of dispersed nanowires?4.23emu/g?at the same temperature.Owing to the larger surface energy restrained the spin flip,the C urie temperature of bundled CoFe₂O₄ nanowires progressed.Finally,CoFe₂O₄/Co₃O₄ and NiO/NiFe2O4 nanocomposites were synthesized used the ordered Co₃O₄ and Ni Fe2O4 nanowires as template by the impregnation method.The exchange bias effect of CoFe₂O₄/Co₃O₄ nanocomposites was easily observed for the interfaces interaction between the antiferromagnetic Co₃O₄ andferrimagnetic CoFe₂O₄,and this phenomenon was obviously observed at 100 K.And Hc increased from 11.4 Oe to 160.1 Oe at 100 K.Meanwhile,the magnetization of CoFe₂O₄/Co₃O₄ nanocomposites increased with the increasing ferromagnetic CoFe₂O₄ nanoparticles.For the NiO/NiFe2O4 nanocomposites,exchange bias effect was observed at 10 K for NiO/NiFe2O4 nanocomposites,and the exchange bias effect enhanced with the NiO content.And Hc increased from 276.1 Oe to 379.8 Oe and 495.4 Oe.Owing to the exchange bias effect,the block temperature?TB?increased with the NiO content.Due to the magnetic dilution,saturation magnetization?Ms?decreased with the increasing antiferromagnetic NiO.