Tailoring the structural and magnetic properties of self-ordered nickel nanowires created by template-assisted electrodeposition route

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.