Preparation And Characterization Of Diameter-graded Magnetic Nanowire Arrays

Fe-Co alloy nanowire arrays were successfully synthesized by direct current(DC)electrodeposition via employing anndic aluminum oxide(AAO)as templates,the nanowire with diameter 20 nm,50nm,100 nm and 20-100 nm diameter-geaded.The as-deposited products were characterized by XRD,SEM,TEM,and VSM to gain the information of microstructure,topography and magnetic performance.FORC was used to gain the information of magnetization reversal.The heterogeneous nanowire was compared with homogeneous nanowires arrays that with same component,to analyzed and studied the special performance of diameter-graded nanowire.The diameter-graded nanowire was prepared by two-step process.Firstly,a high-purity aluminum(99.999%)sheet was anodized under 80 V to perform the first anodization process.In order to form the diameter-graded nanopores,the second anodization was carried out under a staring voltage of 15 V,then ramp to 80 V.The diameter-graded nanochannels were formed due to the gradually increasing voltage.Secondly,on the basis of AAO template with diameter-graded nanopores(fine side),The Al layer was deposited by sputtering before electrochemical deposition under potentiostatic conditions(3V)to fill the pores.The template morphology affected by temperature,concentration of electrolyte,time of secondary oxidation and time of expanding was discussesed in this paper.For the information of VSM,we can concluded that: Forhomogeneous nanowire,the coercivity are decreased with diameter increased,and interaction distribution wider when diameter increased;For diameter-graded nanowire,the coercivity of perpendicular direction approximate to parallel direction,the magnetic anisotropy energy is smaller than homogeneous nanowires,and show a major magnetic.From the information of FORC: the general rule between diameter and type of interaction is that,if diameter was larger than separation(edge to edge),the dominate interaction is exchange interaction,and vice versa.It is worth noting that the end of 20 nm show dipole interaction,and the end of100 nm show exchange interaction of the diameter-graded sample.It is demonstrated that the dominant interaction was changed in diameter-graded nanowire.