Template-assisted Co-Ni alloys and multisegmented nanowires with tuned magnetic anisotropy

Homogeneous Co₈₅Ni₁₅ and Co₅₄Ni ₄₆ alloys, together multisegmented Co₈₅Ni ₁₅/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 Co₈₅Ni ₁₅/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. The study of nanostructured magnetic materials synthesized through electrochemical methods by employing anodic aluminum oxide membranes as patterned templates has recently attracted a huge attention. García et al. have electroplated Co_100-xNi_x (15 ≤ x ≤ 61) alloy nanowires of about 180 nm in diameter into the pores of hard-anodic nanoporous alumina membranes, as well as multisegmented Co₅₄Ni ₄₆/Co₈₅Ni₁₅ nanowires with an approximate length of 300 nm per segment. The magnetic properties of the nanowire arrays were studied and correlated with the microstructural features of each alloyed/multisegmented system.