E.V. Sukovatitsina

High-density nickel nanowire arrays for data storage applications

This paper is dedicated to a study of magnetic properties (magnetic anisotropy, coercive force and remanent magnetization) of spatially ordered high-density Ni nanowire arrays. The magnetic nanowires were prepared by electrodeposition of nickel from simple sulfate solutions into anodic aluminum oxide (AAO) nanoporous templates (with diameter of d = 20 and 40 nm) fabricated by potentiostatic anodization. We show that Ni nanowires have strong out-of-plane axial magnetic anisotropy (normal to the substrate plane) along with an in-plane anisotropy caused by hexagonal spatial distribution of nanowires in an array. An existence of the six-fold in-plane anisotropy proofs the long-range hexagonal order of nanowires. High quality of nanowire arrays makes possible of its usage as high-density (up to 2Tb/in2) magnetic recording media.

Electrodeposited Co93.2P6.8 nanowire arrays with core-shell microstructure and perpendicular magnetic anisotropy

We demonstrate the formation of an unusual core-shell microstructure in Co93.2P6.8 nanowires electrodeposited by alternating current (ac) in an alumina template. By means of transmission electron microscopy, it is shown that the coaxial-like nanowires contain amorphous and crystalline phases. Analysis of the magnetization data for Co-P alloy nanowires indicates that a ferromagnetic core is surrounded by a weakly ferromagnetic or non-magnetic phase, depending on the phosphor content. The nanowire arrays exhibit an easy axis of magnetization parallel to the wire axis. For this peculiar composition and structure, the coercivity values are 2380 ± 50 and 1260 ± 35 Oe, parallel and perpendicular to the plane directions of magnetization, respectively. This effect is attributed to the core-shell structure making the properties and applications of these nanowires similar to pure cobalt nanowires with an improved perpendicular anisotropy.

Magnetic Behavior of Single Ni Nanowires and its Arrays Embedded in Highly Ordered Nanoporous Alumina Templates

We report on magnetization reversal and geometry dependent magnetic anisotropy of Ni nanowire arrays electrodeposited in nanoporous alumina templates. Using micromagnetic simulation we have found that magnetization reversal mechanism in arrays with different nanowire diameters is curling. This magnetic behavior appears with propagation of the domain wall along a nanowire. The calculations have been proven by the analysis of hysteresis curves. To explain magnetic properties of closely-spaced nanowire arrays we have taken into consideration the magnetostatic interaction between adjacent nanowires and their structural defects, like as boundary grains. The investigated magnetic domain pattern of individual bended nanowires confirms rather complicated magnetization reversal mechanism than either coherent rotation of magnetization or its curling. Competition between the shape and magnetoelastic anisotropies can induce an unusual zigzag-like domain pattern in a single nanowire.

Dependence of the magnetic properties of nanocrystalline nickel films on grain size and surface morphology

Nickel films prepared by direct-current, pulse-current, and pulse reverse-current electrodeposition are studied. Scanning electron microscopy and atomic force microscopy show that the films consist of fine grains. The electrodeposition conditions are varied to prepare films with different grain sizes and surface roughness. All the films are magnetically isotropic. In films with a grain size comparable to the width of Bloch domain walls, the magnetization reversal occurs owing to the incoherent rotation of magnetization. In films with a grain size of more than 350 nm, the magnetization reversal occurs not only through the incoherent rotation of magnetization, but also owing to the nucleation and displacement of the domain walls.

Magnetic Properties of Electrodeposited Nickel-Multiwall Carbon Nanotube Composite Films

Coelectrodeposition of Ni with multiwall carbon nanotubes (MWCNTs) was successfully carried out by noncovalent functionalization. Microstructure and magnetic properties of Ni-matrix nanocomposites films were investigated in a range of MWCNTs content from 2% to 5.1%. The MWCNT content was controlled by current density and MWCNT concentration in the solution. Ni-matrix composite films exhibit polycrystalline microstructure having different texture factors along (111) and (200) crystallographic orientations. The nanocomposites films show in-plane easy axis of magnetization. However, coercivity and squareness variations imply that magnetocrystalline anisotropy, grain size, and morphology as well as Ni/carbon nanotube interfacial microstrain play crucial roles in the magnetization process.

Crystal structure and coercivity of electrodeposited nickel films

We report on an experimental study on electrodeposited nanocrystalline nickel films. Scanning electron and atomic force microscopies reveal granular structure of the films with varying grain size and surface roughness in dependence on deposition conditions. In term of magnetic properties all the fabricated films are isotropic. We define magnetization reversal occurring through the non-coherent magnetization rotation where the average grain size is comparable to the width of Bloch domain walls (DW). For those film with a greater grain size, the remagnetization processes take place due to the non-coherent magnetization vectors rotation and DW displacement in the grains.

An influence of mechanical deformations on crystal structure and spin configuration in magnetic nanowires

The influence of strain induced into individual fine-grain Ni nanowires on crystalline and magnetic structures is discussed in this paper. Using transmission electron microscopy, we have found that the crystal twinning occurs in the strained parts of the nanowires. Changes in crystalline structure due to the mechanical deformations induce a magnetic anisotropy, which leads to a transverse magnetic structure.

Microstructure evolution and magnetic behavior of self-organized arrays of ultra-high aspect ratio epitaxial Co nanostrips

The arrays of magnetic nanowires (NWs) and nanostrips (NSs) with uniaxial anisotropy are good candidates to be used in domain wall propagation based devices, magnetic storage media with high recording density, GMR sensors and biomedical assays [1,2].

Magnetic properties of electrodeposited nickel-MWCNT nanocomposite films

Ni-MWCNT nanocomposite films are prepared in this study by electrodeposition. Scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy are used to determine the microstructure and composition of the nanocomposite films. Magnetic hysteresis loops and magnetization curves are recorded in different configurations to clarify behaviors of magnetic anisotropy, coercivity, magnetization reversal, and domain wall motion.

Composition-dependent reorientation of magnetic anisotropy in electrodeposited CoNi nanowire arrays

Magnetic nanowires embedded in a porous template are under high attention of scientists because of the promising electronic applications. Electrodeposition enables one to fabricate magnetic “nanowired” substrates (MNWS), which are ideal candidates for high frequency utilizations due to their desirable materials properties and the possibility to build tunable nanomagnetic devices applicable for a tailored frequency range. Manipulation of the nanowire composition allows changing the crystal structure leading to the rotation of easy axis (e.a.) of magnetization in the arrays. In this paper, we report on the composition-dependent reorientation of magnetic anisotropy in CoNi nanowire arrays electrodeposited into an anodic alumina template using different deposition frequencies and electrolytes. Dimensionality and micromagnetic characteristics of the nanowire arrays with different orientation of magnetic anisotropy have been determined with processing of magnetization curves with approach to the magnetic saturation law.