Tuning the coercivity of Fe-filled carbon-nanotube arrays by changing the shape anisotropy of the encapsulated Fe nanoparticles

Abstract

To tune the coercivity of Fe-filled carbon-nanotube (CNT) arrays, the shape anisotropy of encapsulated Fe nanoparticles (Fe-NPs) was investigated. Four Fe-filled CNT-array samples with different Fe-NP aspect ratios were prepared by catalytic pyrolysis of acetylene using ferrocene as catalyst. The coercivity of the Fe-filled CNT arrays increased from ∼300 to ∼800 Oe at room temperature when the mean aspect ratio of the encapsulated Fe-NPs changed from 1.6 to 6.0. This clear dependence of the coercivity of the Fe-filled CNT arrays on the aspect ratio of the Fe-NPs might be interpreted in terms of the Stoner–Wohlfarth model. This result indicates that changing the shape anisotropy of the encapsulated Fe-NPs is an effective method to tune the coercivity of the Fe-filled CNTs.