No abstract

Meniscus-confined electrodeposition (MCED) is an effective and versatile technique for fabrication of alloy structures with precise localization and high controllability. Here, the fabrication of cobalt-copper (Co/Cu) alloy microwires using MCED techniques is reported. Co/Cu microwires with a wide range of compositions (Co9Cu91 to Co100Cu0) and controllable morphology were printed using the co-electrodeposition mode from a single electrolyte. We utilized multiphysics finite element simulation to investigate the influence of electrolyte evaporation and electric field on the concentration distribution of metal ions in the meniscus. The concentration of ions at the substrate interface increases linearly with decreasing humidity and increasing current density, which can be used to fine turn the alloy composition. By further analyzing the alloy composition, we found that the electrodeposition of Cu is diffusion controlled, while Co is mainly electrochemical reaction controlled, as a results of combined action of surface evaporation and reaction dynamics in the meniscus. The prepared alloy wires are polycrystalline, dense and uniform composition distribution. The coercivity and magnetic anisotropy are enhanced by increasing of the copper content in the alloy wires. The high tunability of composition make this alloy a promising material for magnetic micro/nano-electromechanical devices.

recording due to their high aspect ratio, high coercivity, and high storage density. [6] Modulating the magnitude of the coercivity and the saturation magnetization by combining magnetic materials and pure metals was initially developed in 1978 to produce binary and ternary alloys. [7] Since then, binary alloys have attracted widespread attention due to their potential applications in magnetoresistive and thermoelectric devices. [8] In recent years, the influence of morphology [9] and composition [10] inhomogeneity on magnetic alloy micro/nanowires has been studied extensively. But the preparation of ordered gradient micro/nanowires with controllable diameters and compositions is still a major problem.The gradient magnetic anisotropy is so far mainly achieved by changing the material shape of a single metal micro/ nanowire, [11] or by changing the material composition of alloy micro/nanowires. [12] The anodic aluminum oxide (AAO)-templated electrodeposition method [9] is the most commonly used method for mass production of gradient micro/nanowires. Prida et al. [13] employed a SiO 2 -coated hard AAO membrane as the template for electrochemical growth of multisegmented Co-Ni nanowire arrays by alternately varying between two different deposition potentials. Magnetic anisotropy is realized with the prepared wire arrays due to the alternating composition and crystalline structure of the individual segment. To realize shape gradient, Arzuza et al. [14] combined the three-step anodization with an intermediate chemical etching step to modulate the wire diameter.Gradient magnetic micro/nanowire arrays have attracted widespread attention due to their interesting properties. However, fabricating such an ordered array of gradient micro/nanowires with controllable diameters and compositions is still a great challenge to most of the current methods. Here, meniscus-confined electrodeposition (MCED) technique is adopted for the rapid prototyping of the shape-gradient magnetic Cu/Co-alloy microwire arrays by adjusting the printing speed continuously, which provides a novel idea for the preparation and performance research of shape-gradient magnetic alloy microwire arrays with well-defined structures. It is found that the key to fabricating controllable gradient alloy micro/nano structures by increasing the printing speed is to continuously stretch the meniscus within the stable range of the meniscus. In the range of incremental speed in this study, the shape-gradient magnetic alloy wires with stable and uniform compositions and dense internal structures can be successfully prepared, and the gradient ratio can be adjusted from 0 to about 0.025. Compared with the uniform-diameter array, the shape-gradient magnetic alloy array shows an improvement in remanence and coercive force.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admt.202200024.