Synthesis and properties of iridescent Co-containing anodic aluminum oxide films

• Iridescent Co-containing anodic aluminum oxide films were successfully fabricated.
• Magnetic results indicate that the coercivity is as high as 1.2 × 105 A/m.
• Magnetization reversal mechanism is in good agreement with coherent rotation model.
• Such colored films could be used in multifunctional anti-counterfeiting applications.

A simple method of fabricating Co-containing anodic aluminum oxide films for multifunctional anti-counterfeit technology is reported. The films display highly saturated colors after being synthesized by an ac electrodeposition method. Tunable color in the films is obtained by adjusting anodization time, and can be adjusted across the entire visible range. Magnetic measurements indicate that such colored composite films show excellent magnetic properties. The resulted short (310 nm in length) and wide (50 nm in diameter) Co nanowires present only hexagonal close-packed phase, with the coercivity and squareness ratio as high as 1.2 × 105 A/m and 0.803, respectively. The magnetization reversal mechanism is in good agreement with coherent rotation model. The color and magnetic properties remain the same over a wide temperature range. The Co-containing anodic aluminum oxide films with structural color and perpendicular magnetic recording properties have friability-resistant feature and could be used in many areas including decoration, display and multifunctional anti-counterfeiting applications.

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