Growth and characterization of Ni_xCu_1_-_x alloy films, Ni_xCu_1_-_x/Ni_yCu_1_-_y multilayers, and nanowires

Abstract

It was found that it is possible to grow Ni_xCu_1_-_x alloy systems of arbitrary composition by electrodepositing well-defined sub-monolayer quantities of Ni and Cu in alternation using a new method based on that used previously to prepare potentiostatically deposited magnetic multilayers from a single sulphamate-based electrolyte. Following growth, the chemical composition of Ni_xCu_1_-_x alloy films was obtained by ZAF-corrected energy dispersive X-Ray (EDX) analysis and less than a 4% difference between the nominal and actual composition was observed. The structure of the films was investigated by high-angle X-ray diffractometry (HAXRD) and transmission electron microscopy (TEM). The films grown on polycrystalline Cu substrates had (100) texture, while those grown on Au-coated glass had (111) texture. Some evidence of Ni clustering was obtained by vibrating sample magnetometry (VSM). Self-organisation of the deposited metal was suggested for Ni potentials more positive than #approx#-1.4V. The transition from a Ni/Cu multilayer to a Ni_xCu_1_-_x alloy was also studied and an interesting aspect, namely a plateau region in a plot of magnetisation as a function of Ni layer thickness was observed, suggesting a preferred Ni cluster size in these alloy films. Anisotropic magnetoresistance (AMR) of the films decreased with increasing Cu content at 300K and 77K. SQUID measurements for Ni_0_._5_2Cu_0_._4_8 and Ni_0_._6_2CU_0_._3_8 films showed that they become much more strongly ferromagnetic at low temperatures. Evidence for blocked -superparamagnetic behaviour above a blocking temperature (T_B) of the films was obtained from zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibility measurements. Ni_xCu_1_-_x/Ni_yCu_1_-_y alloy/alloy multilayer films with short repeat distance were successfully fabricated using this method. Up to third order satellite peaks observed in HAXRD showed that the interface is sharp. Room temperature longitudinal magnetoresistance measurements showed that Ni_xCu_1_-_x/Ni_yCu_1_-_y multilayers with certain layer thicknesses and compositions exhibit giant magnetoresistance (GMR) at room temperature which switched to AMR at 77K. This is a magnetotransport behaviour that is only possible through materials engineering. As another application of the new pulse-plating method Ni_xCu_1_-_x alloy nanowires were successfully electrodeposited into nuclear track-etched polycarbonate membranes. The current profiles recorded during deposition showed three different stages of growth: nucleation onto the Au substrate, steady growth in the pores, and growth of the wires in three dimensions. The structural analysis of the nanowires by TEM showed the grain length varied in the range 5-100nm, while its width varied between a few nm and the full width of the wire. The actual length and diameter of the wires were measured to be #approx#5#mu#m and (80#+-#5)nm respectively. The chemical compositions of the nanowires were obtained by EDX analysis. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN049385 / BLDSC - British Library Document Supply CentreGBUnited Kingdo