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Thin films of vertically oriented self-ordered nickel nanowires were fabricated using the template-assisted electrodeposition method. Magnetic measurements of as-formed nanowires revealed the presence of an axial easy magnetization direction due to the shape of the nanowires. At moderate annealing temperatures, the magnetic anisotropy changed from positive to negative. This indicated easy magnetization direction flipping from axial to radial configuration. A nickel oxide phase started to grow at higher annealing temperatures with a distinct reduction in saturation magnetization due to its antiferromagnetic character. In addition, an exchange bias was observed owing to the coexistence of ferromagnetic and antiferromagnetic phases. Single-phase nickel oxide nanowires were generated at elevated annealing temperatures and exhibited an unexpected ferromagnetic behavior attributed to the incorporation of nickel ions and oxygen vacancies as suggested by ferromagnetic resonance measurements. Diffuse reflection measurements indicated an effective energy gap of 4.2 eV for nickel oxide nanowires. [ABSTRACT FROM AUTHOR]

The local microstructure of Fe–Ga nanowires is investigated considering dependence on the deposition technique. Using a complexed electrolyte, smooth and homogeneous Fe80Ga20 nanowires are deposited into anodic aluminum oxide templates by either applying pulse potential or potentiostatic deposition technique. At optimized deposition conditions the wires show the desired composition of Fe80±2Ga20±2 without a gradient along the growth direction. Composition distribution, structure and microstructure are examined in detail and reveal only minor differences. Line EELS and crystal lattice measurements reveal a negligible oxygen content for both preparation routines. Neither Fe/Ga oxides nor hydroxides were found. Both potentiostatically deposited as well as pulse deposited nanowires exhibit a preferred 〈110〉 orientation, the latter with slightly larger crystals. Different contrast patterns were found by TEM that appear more pronounced in the case of pulse deposited wires. High resolution transmission electron microscopy analysis and comparison of differently prepared focused ion beam lamellas reveal that these contrasts are caused by defects in the alternating potential deposition itself and are not induced during the TEM preparation process. The alternating potential mode causes periodic growth thereby inducing different layers with reduced wire thickness/defects at the layer interfaces. [ABSTRACT FROM AUTHOR]

Herein, the magnetic vortex domain wall structure of polycrystalline imperfect iron−cobalt alloy nanowires (Nws) growing on 1050 aluminum by pulsed electrodeposition is reported. The magnetic properties are analyzed using magnetometry and off‐axis electron holography. The electrodeposited Nw arrays show homogeneous elemental composition and exhibit a structure composed of piled‐up grains of small crystallites. The saturation magnetization, coercive field, and reduced remanence, measured in directions parallel and perpendicular to the Nw's axis, are studied as a function of the temperature. Although the array of Nws on anodized aluminum grows both straight and within an inclination angle, in both cases, a high shape anisotropy is noticed, which is the most predominant contribution to the magnetic behavior. Misalignments and defects of the Nws in the array, as well as the wide distribution of lengths and diameters, do not contribute significantly to coercivity dispersion. A modified model is used to explain the changes in the magnetic behavior of the Nw's arrays, which accounts for structural imperfections and magnetostatic interactions. The reversal magnetization arising from the vortex domain wall propagation via localized curling is verified by off‐axis electron holography. [ABSTRACT FROM AUTHOR]

Herein, the structural and magnetic properties of Ni and Co nanowires obtained by electrodeposition on alumina membranes are studied. Structural analysis shows the coexistence of Ni and Co metallic phases as well as NiO and CoO, which are associated with the preparation method. The magnetic study suggests the possibility of unidirectional anisotropy as a possible mechanism on the magnetization reversal in nickel and cobalt nanowires. For the experimental curves of coercivity versus temperature, there exists a critical value, below which only the dipole interactions are predominant. Above this temperature, the dipole magnetocrystalline and magnetostrictive energy compete in a complicated way. Alongside these three contributions, the coexistence of the "local unidirectional coupling" of antiferromagnetic nanoparticles that engage in random directions on nanowires is proposed. [ABSTRACT FROM AUTHOR]

In this work, a successful fabrication of Co2MnAl heusler alloy nanowires in anodic alumina templates has been demonstrated using simple and low-cost electro-deposition technique at room temperature. The role of deposition parameters, such as pH of the electrolyte solution were investigated on the structural and magnetic properties of Co2MnAl nanowires. It is observed that the crystallinity improves with the increase of pH of the solution till around pH=3.0 where the best crystallinity is achieved. The X-Ray diffraction pattern confirms the formation of B2 crystal type in the Co2MnAl heusler alloys which is further verified by high-resolution transmission electron microscope images. The static magnetic properties were explored by the VSM analysis which revealed that the saturation magnetization, squareness, coercivity and uniaxial anisotropy of the nanowires increase with the increase in pH value. The highest remanent squareness of 76% is observed for pH=2.9. The dynamic measurements of heusler alloy nanowires have been studied by ferromagnetic resonance technique using the flip-chip method in the field-sweep mode at different applied frequencies ranging from 20-40 GHz. It is observed that the resonance field increases linearly with the increase in frequency for all samples. Further, the resonance field decreases up to 35% with the increase of pH value of electrolyte, resulting in an increase in the effective field. [ABSTRACT FROM AUTHOR]

Magnetic properties of Fe nanowire arrays (NWs) electrodeposited in anodic alumina membranes have been studied. The influence of nanowire geometry (length, pore diameter) and an external magnetic field applied during electrodeposition process on the magnetic properties of nanowire arrays was investigated. With the use of the X-ray diffraction analysis the structure of iron wires was determined. The iron wires have the regular Body Centered Cubic structure. Magnetic measurements show that shape anisotropy aligns the preferential magnetization axis along the wire axis. It was found that the application of an external magnetic field in a parallel direction to the sample surface induces magnetic anisotropy with an easy axis of magnetization following the nanowire axis. The dependence of the height of Fe wires on the electrodeposition time was determined. [ABSTRACT FROM AUTHOR]

Segmented nanowires (NWs) have found a wealth of applications due to their multifunctionality, arising from complementarities and synergies among segments of different materials. However, to ensure a practical use of segmented NWs, high quality interfaces between segments must be ensured. Herein, trisegmented CoPt/Cu/Ni NWs and bisegmented CoPt/Ni magnetic NWs are fabricated by means of template-assisted electrodeposition and the characteristics of their interfaces are investigated in detail. The presence of a Cu segment sandwiched between the CoPt and the Ni segments severely affects the integrity of the whole NW. Namely, Cu deposits in a (200) textured face-centered cubic (fcc) structure, which cannot accommodate well on the c-axis oriented hexagonal close-packed CoPt. Instead, when the Cu segment is absent, well-connected CoPt/Ni NWs with smooth interface are obtained. Unlike the Cu segment, Ni shows the (111) textured fcc structure, which holds good crystallographic matching with the underlying CoPt segment. Magnetic measurements reveal that CoPt/Ni NWs exhibit staircase-like hysteresis loops similar to the trisegmented CoPt/Cu/Ni NWs. Such loop shape stems from the dissimilar coercivity between the hard (CoPt) and soft (Ni) segments. The bisegmented NWs (with robust interfaces) are appealing for multibit recording media, magnetic nanoelectromechanical systems, and magnetically driven drug delivery nanoplatforms. [ABSTRACT FROM AUTHOR]

Homogeneous Co85Ni15 and Co54Ni46 alloys, together multisegmented Co85Ni15/Co54Ni46 magnetic nanowire arrays have been synthesized by means of potentiostatic and pulsed potentiostatic electrodeposition techniques, respectively, into the pores of hard-anodic alumina templates. Morphological, compositional and structural characterization indicate that the composition of Co-Ni alloy segments and nanowires can be properly adjusted by varying the electrochemical deposition potential, leading to different crystalline structures (fcc or hcp) depending on the Co-Ni alloy composition. The magnetic properties of homogeneous and multisegmented Co-Ni alloy nanowire arrays, obtained from hysteresis loops and switching field distribution calculations, are correlated with their crystalline structure and effective magnetic anisotropy, to shed light on the magnetization processes that determine the magnetic behaviour of the nanowire arrays. Part (a) shows a schematic drawing of freestanding multisegmented Co85Ni15/Co54Ni46 nanowires. Part (b) displays the magnetic hysteresis loops of multisegmented nanowire arrays measured along the parallel and perpendicular directions with respect to the nanowires long axis. [ABSTRACT FROM AUTHOR]

FePd nanowires (NWs) with different compositions have been grown into anodized aluminum oxide templates (AAO) by AC electrodeposition at room temperature. The effects of nanowire composition and morphology on the hysteresis properties of the ordered array of NWs are investigated. All the NWs are polycrystalline; the Fe-rich wires have a bcc structure while the Pd rich ones are fcc. FePd NWs are ferromagnetic and the spontaneous magnetization is found to be parallel to the nanowire long axis (out of plane easy axis) and both, the saturation polarization and the coercive field increase with the iron content. [ABSTRACT FROM PUBLISHER]

A cylindrical magnetic nanowire system composed of ferromagnetic core and shell layers has been investigated by using effective field theory (EFT) with correlations. Both ferromagnetic and antiferromagnetic exchange couplings at the core-shell interface have been considered. Main attention has been focused on the effects of the quenched disordered shell bonds, as well as interface bonds on the magnetic properties of the system. A complete picture of the phase diagrams and magnetization profiles has been represented. It has been shown that for the antiferromagnetic nanowire system, the magnetization curves can be classified according to Néel theory of ferrimagnetism and it has been found that under certain conditions, the magnetization profiles may exhibit Q-type, P-type, N-type, and L-type behaviors. The observed L-type behavior has not been reported in the literature before for the equilibrium properties of nanoscaled magnets. As another interesting feature of the system, it has been found that a compensation point can be induced by a bond dilution process in the surface. [ABSTRACT FROM AUTHOR]