The pH Rule for Fabricating Composite CoCu Nanowire Arrays

tion and characterization of composite CoCu nanowires. The magnetic properties of the composite Co-based nanowire should be much better than the single phase nanowires, because more boundaries and grain surfaces can improve the effective aniso- tropy and enhance the magnetic coercivity. In this paper, a series of CoCu electrodepositing experi- ments have been carried out under the different pH values and potentials. We found that the structure and the composition dependences exhibit a strong pH value rule: 1) the nanowires with wider composition range can be prepared by using a moderate pH value of 3.3; 2) using this pH value, the nanowires are of composition with hexagonal close packed (hcp) and fcc structures. Due to containing rich phase boundaries, the magnet- ic properties of the nanowire arrays apparently precede to those in single phase samples. Nanoporous anodized alumina oxide (AAO) templates with diameter of 50 nm were prepared by a two-step anodization process. The CoCu nanowires were electrodeposited into the pores by DC electrolysis in an electrolyte consisting of 0.08 M CoSO4, 0.008 M CuSO4 (Co 2þ :Cu 2þ = 10:1), and 0.5 M H3BO3. The pH 3.1, 3.3, and 3.5 are adjusted by adding NaOH solution. The electrodeposition of Co1 xCux nanowires was carried out at different depositing potentials ( 1:0 to 1:4 V) at given pH values. The chemical compositions of the nanowires were determined by energy-dispersed X-ray spectrometry (EDXS), the microstructure and magnetic properties were detected by transmission electron microscopy (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). A series of Co1 xCux nanowire arrays have been obtained by electrodeposition in the AAO templates. The nanowires are all straight and parallel to each other with uniform diameter of 50 nm and total length of about 15-20 mm. Table 1 shows the Co1 xCux composition and structure de- pendence of pH values and depositing potentials. The Cu content is in a large composition range of x ¼ 0:05{0:70 and monoto- nously increases with the increase of the depositing potential. The fact that Cu rich samples (for example, Co0:30Cu0:70) still can be deposited in these rich Co 2þ solutions implies that the depositing rate of Cu is much higher than that of Co. This result was also reported in previous works. 3,5