Controlling structural and magnetic properties in CoNi and CoNiFe nanowire arrays by fine-tuning of Fe content

Abstract

Herein, Co70Ni30 and CoxNiyFez (45 ≤ x ≤ 70; 22 ≤ y ≤ 33; 5 ≤ z ≤ 30) nanowire (NW) arrays with a length of
approximately 15 μm and diameter of 30 nm have been fabricated using a pulse electrochemical deposition
technique in anodic aluminum oxide templates. Increasing the Fe additive concentration (ranging between
0.0035 and 0.05 M) in electrolyte solution has a considerable effect on the composition and crystalline
characteristics of the resulting NW arrays, changing the hcp-Co and fcc-Ni phases into the bcc-Fe phase in
Co45Ni25Fe30 NWs. On the other hand, hysteresis curves obtained from Co70Ni30 NWs show that, while the
average coercivity (Hc
Hyst) of parallel and perpendicular applied fields is nearly the same (Hc
Hyst~ 400 Oe),
the corresponding squareness ratio is greater in the latter case, indicating a perpendicular anisotropy of NWs.
Changing the Fe content in the range of 8-11% causes shape anisotropy to dominate the CoNiFe NW system
with the bcc-Fe crystalline phase, allowing for controllable magnetic properties. The advanced analysis of
angular first-order reversal curves (AFORCs; 0° ≤ θ ≤ 90°) revealed that the FORC coercivity (Hc
FORC) in
Co62Ni29Fe9 NWs increases from 700 Oe at θ= 0° to 950 Oe at θ= 90°, thereby evidencing a vortex domain
wall mode (VDW). However, for Co55Ni22Fe23 NWs with a dominant bcc-Fe phase, Hc
FORC reaches 2700 Oe
at θ= 77°, starting from 1400 Oe at θ= 0°. In addition to occurring the VDW mode, a single vortex appeared
in the Co55Ni22Fe23 NWs when 68° ≤ θ ≤ 77°, followed by its annihilation for θ> 77°