Preparation,Mechanical And Magnetoelectric Properties Of BiFeO₃ And CoFe₂O₄ Based Multiferroic Composite Nanofibers

Multiferroic materials are the multi-functional materials with two or more types of ferroic orderings coupling among（anti）ferroelectric,（anti）ferromagnetic and ferroelastic simultaneously,which have attracted a great deal of attention in the past few years.The magnetoelectric coupling makes the multiferroic materials promising for a wide range of applications including magnetic sensors,transducers,modulated microwave and memories,and much of the attention has been focused on the composite multiferroic materials.Because of the unique structure,one-dimensional nanofibers have the excellent properties such as high specific modulus,high specific strength,specific surface area,compact structure,high toughness,size effect and interface effect,easy integration and miniaturization.Compared with multiferroic thin film,the constraint of the substrate on the nanofibers could be substantially relaxed.The large aspect ratio of the nanofibers also makes it possible to magnify the mechanical displacement due to the piezoelectric or magnetostrictive effect,and thus enhance the magnetoelectric coupling even further.In this paper,one-dimensional multiferroic magnetoelectric materials were investigated.One-dimensional multiferroic composite nanofibers with BiFeO₃ as ferroelectric phase were prepared by sol-gel based electrospinning.The preparation parameters,mechanical properties and magnetoelectric properties of the multiferroic composite nanofibers were studied.The main research findings are summarized as follows:（1）BiFeO₃（BFO）,CoFe₂O₄（CFO）and BFO/CFO random composite nanofibers with different molar ratios were prepared by electrospinning.Amplitude modulationFrequency modulation（AM-FM）mode based on Atomic Force Microscopy and nanoindentation were used to study the mechanical properties of those nanofibers,respectively.The observed results show that the elastic modulus and hardness for BFO nanofibers are 52.5 ± 5.1 GPa and 1.6 ± 0.4 GPa,respectively.The corresponding values for CFO nanofibers are 146.2 ± 5.3 GPa and 9.2 ± 0.3 GPa.Further,The elastic modulus and hardness of the composite nanofibers increaseing with the increased CFO content.（2）Series magnetoelectric composite nanofibers with Janus structure were fabricated by parallel electrospinning,and the magnetoelectric coupling of obtainednanofibers were studied by PFM.The results show that the nanofibers prepared by self-made parallel needles are composed by two parallel fibers.The amplitude and frequency response of the fibers on either sides are obviously different,and the magnetoelectric coupling was observed in the composite fibers.（3）The BFO parallel nanofiber arrays were prepared by two static parallel electrode and rotated hollow cylinder respectively,and the orientation of the fibers was observed by metallographic microscope.The results show that the uniformity of parallelism BFO nanofibers obtained from parallel electrode are better than that obtained from rotated hollow cylinder.The optimized electrospinning parameters when using static parallel electrode as the collecting device are as following: voltage is 6 kV,electrode spacing is 6 cm,receiving distance is 7 cm,propulsion speed is 0.7mL/h.