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.

Highly hexagonally ordered hard anodic aluminum oxide membranes, which have been modified by a thin cover layer of SiO2 deposited by atomic layer deposition method, were used as templates for the synthesis of electrodeposited magnetic Co-Ni nanowire arrays having diameters of around 180 to 200 nm and made of tens of segments with alternating compositions of Co54Ni46 and Co85Ni15. Each Co-Ni single segment has a mean length of around 290 nm for the Co54Ni46 alloy, whereas the length of the Co85Ni15 segments was around 430 nm. The composition and crystalline structure of each Co-Ni nanowire segment were determined by transmission electron microscopy and selected area electron diffraction techniques. The employed single-bath electrochemical nanowire growth method allows for tuning both the composition and crystalline structure of each individual Co-Ni segment. The room temperature magnetic behavior of the multisegmented Co-Ni nanowire arrays is also studied and correlated with their structural and morphological properties.

The magnetic properties of low dimensional materials of several iron oxyhydroxyde phases, such as akaganéite (β-FeOOH) or lepidocrocite (γ-FeO(OH)), remain poorly explored; probably due to their specific preparation as single crystalline phase requires special conditions owing to their structural instability. In the present work, ultra-fine akaganéite nanoparticles were prepared by the hydrolysis of FeCl 3 solutions at room temperature induced by the presence of NaOH. The resulting product was characterized by several analytical techniques. Structural investigations using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) revealed that the sample was mainly constituted by rather-equiaxial akaganéite nanocrystals with mean diameter of 3.3 ± 0.5 nm. In addition, a small amount of rod-like akaganéite particles with 23 ± 5 nm in length and 5 ± 1 nm in width was also detected. The study of the respective dependences of the dc magnetization and the ac susceptibility on temperature and exciting magnetic field revealed complex magnetic relaxation processes, high coercivity values at low temperature and exchange bias effect. These results have been tentatively explained considering size distribution effects and the presence of superparamagnetic and spin glass-like contributions arising from the frustration of the antiferromagnetic order owing to surface effects and an insufficient filling of the akaganéite channels with Clanions.

Cylindrical nanowires made of Co2FeSn Heusler alloy with high spin polarization have been synthetized via template-assisted electrochemical deposition in nanoporous anodic alumina membranes. Their microstructure and morphology have been characterized by in situ studies of X-ray diffraction, together with scanning and transmission electron microscopy techniques. The basic structural and magnetic characterization revealed a B2-type cubic ordered Heusler structure with a lattice parameter of around 5.8 Å and the [110] direction, preferably aligned with the longitudinal axis of the polycrystalline nanowires. The easy magnetization axis is parallel to the nanowire’s axis too. The point-contact Andreev reflection spectroscopic measurements performed on the nanowire’s fresh surface released high polarization values, that is, P = 0.85–1, and prove that the high spin polarization or half-metallicity will be preserved in the nanoscale regime. The presented results open the possibilities toward future exploration of Heusler nanowires with high spin polarization, which are promising materials for applications in spintronics and high-density magnetic data recording.

Arrays of Co (100-x) Cu (x) (0 ≤ x ≤ 27) nanowires with 45 nm of diameter and 18 µm in length, have been potentiostatically electrodeposited into the hexagonally self-assembled nanopores of anodic alumina membranes. The structural characterization of Co-Cu nanowires confirms the coexistence of both hcp and fcc crystalline phases, with textures that are strongly affected by the fractional content of Cu. Parallel magnetic studies of the room temperature magnetization process by First Order Reversal Curve (FORC) analysis and the angular dependence of coercivity, confirm the presence of two coexisting ferromagnetic phases at intermediate Cu content nanowires, ascribed to a softer magnetic phase for pure Co and a harder magnetic one for the Co-Cu composition alloy, respectively. The temperature dependence of coercivity and remanence reveal a reorientation of the effective magnetic anisotropy with adding Cu into the Co-Cu alloy nanowires, being enhanced by the coexistence of the two ferromagnetic phases.