Electrochemical Preparation And Magnetic Property Of Cu/Ni Multilayered Nanowire By Single-bath Method

Multilayered nanowires are ideal structures to study giant magnetoresistance in the current perpendicular to the plane (CPP-GMR) geometry. They are useful to determine different parameters of materials, such as the spin diffusion length (SDL) and spin scattering asymmetry coefficient, and also significant to explain the mechanism of the giant magnetoresistance effect.In this paper, anodic aluminum oxide (AAO) was used as the template, and the aperture of the AAO template could be changed according to demands by adjusting the technologic parameters of anodization voltage. The Cu/Ni multilayed nanowire arrays were successfully prepared by electrodeposition into the pores of AAO template in a single bath. SEM images revealed that the surface of the nanowire was smooth, which corresponded to the pore size of the used AAO template. Multilayered structure could be easily seen in the TEM images with the interface of Cu and Ni clear. By precise control of the pulse potential and the duration time, the average growing speed of Cu layer could be fixed to 1nm/s, Ni layer could also reach 1.25nm/s. Consequently, desired layer thicknesses were got.Hysteresis loops showed that the coercive force and squareness of all the Cu/Ni multilayered nanowire arrays were smaller than the Ni nanowire arrays. When the aspect ratio of the Ni segment was more than 1, the easy axis was paralled to the wire axis. Otherwise, the easy axis was perpendicular to the wire axis. The squareness (0.415) and coercive force (241Oe) of the Cu/Ni multilayered nanowire arrays with 120nm diameter were obviously enhanced compared to those of the arrays with 80nm diameter. Besides, it was indicated that the magnetic properties of the samples prepared in single-bath were not as good as those prepared in dual-bath.The CPP-GMR values of Cu/Ni multilayered nanowire arrays were measured, when the thickness of Cu segment was fixed to 8nm, GMR decreased after achieving its maximum value 3.8% along with the increase of the Ni segment thickness, which deduced that the SDL of Ni was 65nm at 305K, and the calculated spin scattering asymmetry coefficientβfor Ni segment was 0.06 by the VF model. When the thickness of Ni segment was fixed to 62nm, the GMR reduced rapidly with the increase of the Cu segment thickness. Once the Cu segment was thicker than 10nm, there was no remarkable GMR change. Three kinds of Cu/Ni multilayered nanowire arrays with diameter of 80nm, 120nm and 160nm respectively were compared, and it showed that the GMR value increased first and then decreased with the increase of the diameter. Cu[5nm]Ni[62nm] displayed the best GMR property in this study with GMR up to 42.6% and the saturation field of 3000Oe. The sensitivity was 0.014%/Oe.