Synthesis of crystalline CoFex nanowire arrays through high voltage pulsed electrochemical deposition

• High voltage pulsed electrochemical deposition technique (−50 V) is employed.
• Nanowire arrays exhibit high coercivities (>1600 Oe).
• Crystallites with high crystallinity and different growth orientations are discovered in the nanowires.
• The high-energetic reduced atoms can stack on the usually reported (110) plane together with (111) or (211) plane.
• The shape difference between two magnetization hysteresis loops is due to dipolar magnetostatic interaction.

A high voltage pulsed electrochemical deposition (50 Hz, −50 V) technique was used to synthesize CoFex (x=1.57, 2.02) nanowire arrays in anodic aluminum oxide templates. The nanowire arrays (NA) are different in diameter (NA A, 40 nm; NA B, 50 nm), center-to-center distance (NA A, 60 nm; NA B, 100 nm) and length (NA A, 4 μm; NA B, 8 μm). Microstructural characterization shows high crystallinity of the formed nanowires. The magnetic measurements indicate that the nanowire arrays possess uniaxial anisotropy with the easy magnetization axis along the nanowire. When magnetic field is applied in this direction, the coercivities of both nanowire arrays are larger than 1600 Oe. The shape difference between two magnetization hysteresis loops is due to dipolar magnetostatic interaction, and analytical calculation is performed to interpret the magnetic properties as a function of the wire geometry. The results suggest that during high voltage electrodeposition, reduced atoms are highly energetic and the crystallographic growth planes can be (110), (111) and (211).