Large magnetic anisotropy enhancement in size controlled Ni nanowires electrodeposited into nanoporous alumina templates

Abstract

A large enhancement of the magnetic anisotropy of Ni nanowires (NWs) embedded in anodic aluminium oxide porous membranes is obtained as a result of an induced magnetoelastic (ME) anisotropy contribution. This unusual large anisotropy enhancement depends on the diameter of the NWs and exceeds the magnetostatic (MS) contribution. As a consequence, it leads to effective magnetic anisotropy energies as large as 1.4 × 10(6) erg cm(-3), which are of the same order of magnitude and comparable to the MS energies of harder magnetic materials like Co NWs. Specifically, from ferromagnetic resonance experiments, the magnetic anisotropy of the NWs has been observed to increase as its diameter is decreased, leading to values that are about four times larger than the corresponding value when only the MS anisotropy is present. Our results are consistent with the recently proposed growth mechanism of Ni NWs that proceeds via a poly-crystalline stage at the bottom followed by a single-crystalline stage with texture [110] parallel to the axis of the NWs. A strong correlation between reducing the diameter of the NWs with the decrease of the length of the poly-crystalline segment and the enhancement of the effective magnetic anisotropy has been shown. Magnetization curves obtained from alternating gradient magnetometry experiments show that the average ME anisotropy results from the competition between the magnetic anisotropies of both crystalline segments of the NWs. Understanding the influence of size and confinement effects on the magnetic properties of nanocomposites is of prime interest for the development of novel and agile devices.

Magnetic Nanowires

“…As expected, H MC is negative and increases toward the observed limiting value for pure Co networks with perpendicular c-axis as the Ni content is reduced. It is worth mentioning that the small negative anisotropy contribution observed for the Ni sample could be originated by residual stresses due to the reduced diameter of the nanowires, as recently suggested [87]. Figure 12e shows the anisotropic magnetoresistance ratio (AMR) vs. Ni content (x) at T = 20, 150 and 290 K for the different Ni x Co 1-x CNW networks (See [61,62] for more details on the estimation of AMR ratio in such CNWs).…”

Preparation of Ni Nanowires Covalent Organic Framework Composites with High Electrochemical Stability and Supercapacitor Performance

“…The general methods for synthesizing NiNWs are the template method and the chemical reduction method. 26 Tettamanti et al reported the incorporation of nickel nanowires in graphite-based composites to construct nanostructured platforms that are active in the nonenzymatic oxidation of ethanol. Carbon paste electrode material (CPE-NiNWs) demonstrated very good short-term stability, proving outstanding long-term stability, and allowing its use for at least 60 days.…”

“…Nickel Nanowires (NiNWs) can be obtained by size modulation with a large aspect ratio, which makes it easier to form bridging structures in composite materials with reasonable electrical conductivity and high thermal and chemical stability. − For nanostructured materials, changes in the microstructure have a significant effect on their properties. The general methods for synthesizing NiNWs are the template method and the chemical reduction method . Tettamanti et al reported the incorporation of nickel nanowires in graphite-based composites to construct nanostructured platforms that are active in the nonenzymatic oxidation of ethanol.…”

Orientation Growth and Magnetic Properties of Electrochemical Deposited Nickel Nanowire Arrays

“…Among these methods, template-assisted electrodeposition is a popular way to obtain uniform and highly ordered nanowire arrays [12,13]. The nucleation and growth kinetics of the nanowire arrays in one-dimensional confined geometry can be tuned by different experimental parameters, including template dimension, electrolyte properties (pH value, composition, additive, and so on), reaction temperature, applied voltage, and the current density [14][15][16][17]. In our previous work, we demonstrated that current density can influence the growth direction and crystalline quality of electrodeposited semiconductor nanowire arrays, and further change their photoluminescence properties [18,19].…”