Parpartion, Structure And Magnetic Properties Of Nanocrystalline Spinel Ferrite-based Composite Fibers

The preparation,structure and properties for the nanocrystalline spinel ferrite-based composite fibers have been investigated in this work.The nanocrystalline NiFe_2-xSm_xO₄(x=0-0.15) fibers with diameters 0.5 to 2μm and nanocrystalline CoFe_2-xSm_xO₄(x=0-0.2)fibers with diameters ranging from about 100 to 150 nm with nanosized grains below 60 nm have been successfully prepared using the organic gel-thermal decomposition method. Crystalline grain sizes of the NiFe_2-xSm_xO₄ fibers decrease with Sm contents whilst increase with the calcination temperature.The lattice parameter of the grains becomes large with the Sm³⁺ ions doping,however,it tends to become smaller with increasing calcination temperature.The NiFe_1.85Sm_0.15O₄ fibers formed at a low calcination temperature of 550℃shows a superparamagnetical nature.The saturation magnetization of the NiFe_2-xSm_xO₄fibers is decreased by addition of Sm³⁺ ions while increased with the calcination temperature.The coercivity increases with the reduction of Sm contents and increase of the calcination temperature.The CoFe_2-xSm_xO₄(x=0-0.2) fibers obtained at calcination temperatures from 500 to 700℃are characterized with a single ferrite phase.But at a higher calcination temperature(800℃) with a relatively high Sm content(0.15-0.2),the ferrite structure is unstable and the second phase of perovskite structural SmFeO₃ occurs.The crystalline grain sizes of the CoFe_2-xSm_xO₄ fibers decrease with Sm contents,whilst increase with the calcination temperature.SmFeO₃ phase occurs in the composite fibers increase grain sizes of fibers.The saturation magnetization of the CoFe_2-xSm_xO₄ fibers is decreased by addition of Sm³⁺ ions while increased with the calcination temperature.The coercivity increases with the reduction of Sm contents and increase of the calcination temperature.The perovskite structural SmFeO₃ in the nanocomposite fibers may contribute to a high coercivity.The ZAO-coated CoFe_1.9Sm_0.1O₄ferrite composite fibers were successfully prepared by the sol-gel dipping process.The NIR diffusion reflectance ratio of the ZAO-coated CoFe_1.9Sm_0.1O₄ ferrite composite fibers was 34%,compared to the non-coated CoFe_1.9Sm_0.1O₄ ferrite fibers it increased 5%.The magnetic hard-soft CoFe₂O₄-CoFe₂ composite fibers and CoFe₂O₄/Co-Fe composite hollow fibers were successfully synthesized using the sol-gel and partial reduction process.With the increase of alloy content,the grain size of alloy CoFe₂ increases,while the grain of CoFe₂O₄ phase decreases. The magnetic hard(CoFe₂O₄) and soft(CoFe₂) phases for CoFe₂O₄-CoFe₂ composite fibers are well exchange-coupled.With the alloy content in the composite fibers increased,the saturation magnetization increases,while the coercivity decreased.Compared with the single-phase CoFe₂O₄ and CoFe₂ fibers,the remanence of CoFe₂O₄-CoFe₂ composite fibers is larger.For the CoFe₂O₄/Co-Fe composite hollow fibers,the hollow structure only exists in alloy phase fibers.With the reduction temperature increasing,the saturation magnetization increases.After reduction at 300℃,the composite hollow fibers have a largest coercive force,but the coercive force reduces with the reduction temperature increasing.