Enhanced magnetic properties of magneto-electrodeposited Co and Ni nanowires

Highlights

• Successful magnetoelectrochemical synthesis of Co and Ni nanowires on AAO membranes.

• The XRD analysis reveal the growth of highly crystalline and textured Co and Ni nanowires.

• The electrochemical deposition with an AMF B enhances the average atomic percentage of Co and Ni metals into the AAO membrane pores.

• The magnetoelectrodeposition of Co and Ni nanowires that exhibit high shape anisotropies and large hysteresis loops.

Abstract

The present paper examines the influence of an applied magnetic field B (AMF B) on the physical and chemical properties of electrodeposited Cobalt (Co) and Nickel (Ni) nanowires into anodic aluminum oxide (AAO) membranes. The deposition potential and the effect of the AMF B on the mass transport rate of Ni and Co ions to the bottom of the pores were examined using cyclic voltammetry (CV) and current density–time curves. X-ray diffraction (XRD) studies show that the AMF B promotes the growth of Co and Ni into the membrane pores. The AMF B effect on the morphology and chemical composition of the electrodeposited nanowires were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS), respectively. Co nanowires exhibit a high coercive field ${\text{H}}_{\text{c}}$, shape anisotropy, and squareness ratio $\frac{\text{M}}{{\text{M}}_{\text{s}}}$ than those corresponding to Ni nanowires.

Introduction

The fabrication of ferromagnetic materials with nanometric scale and the study of their physical and chemical properties have recently attracted a great technological and scientific interest. Currently, Co and Ni nanowires have garnered considerable attention due to their potential applications including, for example, the energy storage systems [1,2], magnetic and optical media [3,4], sensors [[5], [6], [7], [8]], spintronics [9,10] and heterogeneous catalysis [11,12]. In the magnetic applications, the anisotropy of Co and Ni nanowires has improved performances compared to the bulk material. The shape anisotropy of nanowires can become dominant when they have weak magnetocrystalline anisotropy. This sparked interest to develop a protocol for the synthesis of ferromagnetic nanowires with controlled size because the magnetic properties are strongly depending on the particle size, shape and orientation. Membrane technology is known as a promising technique for making nanowires with significant anisotropy [13]. Several works [14,15] have confirmed that the growth of nanomaterials in a nanoporous membrane improves the magnetic behavior compared to that of a bulk material or a thin film. The electrochemical growth configured as an alternative, economically affordable, environmental and competitive method to synthesize Co and Ni nanowires. In this technique, we can control the growth nature of the nanomaterials and the nanowires length by acting on the electrodeposition time that responds to the choice of the deposition potential [16].

Moreover, many works have been devoted to studying the physical and chemical properties of the ferromagnetic nanowires by the magneto-hydrodynamic effect (MHD), generated by the presence of the AMF B during the electrochemical deposition [17,18]. However, in the electrolytic deposition, the disordered active surface induced a thermodynamic potential thus provides a microstructural transformation of growth on the substrate in relation with the magnetization [19]. Indeed, Ganesh et al. [20] reported on their work the AMF B effect on Ni electrodeposition from nickel sulfate and nickel chloride bath. They have revealed that the increase of the microroughness of Ni deposit decreases the overpotential during the electrochemical reduction of Ni. Moreover, the crystallites deposited electrochemically under AMF B are very fine unlike those deposited in the absence of an AMF B. In their work, Bund et al. [21] have deposited Ni films from nickel sulfate medium with an AMF B up to 0.7 T. They reported that under a constant and homogenous AMF B, uniform and compact deposits were obtained with smaller Ni grains. Within this context, Zieliński et al. [22] investigated the effects of constant magnetic field of 1.2 T on the electrochemical growth of cobalt alloys at constant potential from sulfate bath. They observed that the Co alloys deposited with AMF B exhibit a dense and smoother surface, reduced fractures, and smaller Co grains.

However, many properties of ferromagnetic nanowires synthetized by this technique of electrodeposition still have not been studied completely and this has motivated researchers in magnetism of nanomaterials to focus on this area. Therefore, the main objective of our study is to examine the effect of a perpendicular AMF B to the working electrode on the electrochemical deposition of Co and Ni nanowires and more particularly on their magnetic properties such as anisotropy, coercivity and magnetization.

The present work was performed to exploit X-ray diffraction (XRD), scanning electron microscopy (SEM) and SQUID analysis in order to reveal how the electrochemical growth of Co and Ni nanowires into AAO membranes depends on the AMF B.