Fe₃O₄/TiO₂ Core/Shell Nanotubes: Synthesis and Magnetic and Electromagnetic Wave Absorption Characteristics

Abstract

Fe 3 O 4 /TiO 2 core/shell nanotubes are fabricated via a three-step process. α-Fe 2 O 3 nanotubes are first obtained, and α-Fe 2 O 3 /TiO 2 core/shell nanotubes are subsequently fabricated using Ti(SO 4 ) 2 as a Ti source by a wet chemical process. The thickness of the amorphous TiO 2 shell is about 21 nm. After a H 2 deoxidation process, the amorphous TiO 2 layer changes into crystalline structures composed of TiO 2 nanoparticles with an average diameter of 2.5 nm, and its thickness is decreased to about 18 nm. At the same time, α-Fe 2 O 3 transforms into cubic Fe 3 O 4 . Consequently, crystalline Fe 3 O 4 /TiO 2 core/shell nanotubes can be fabricated through the process above. The measurements of the magnetic properties demonstrate that the Fe 3 O 4 /TiO 2 core/shell nanotubes exhibit ferromagnetic behavior at room temperature, and the Verwey temperature is about 120 K. The eddy current effect is largely reduced and the anisotropy energy is improved significantly for the core/shell nanotubes due to the presence of the TiO 2 shells. The maximum reflection loss reaches −20.6 dB at 17.28 GHz for the absorber with thickness of 5 mm, and the absorption bandwidth with the reflection loss below −10 dB is up to 13.12 GHz for the absorber with a thickness of 2−5 mm. Our results demonstrate that the Fe 3 O 4 /TiO 2 core/shell nanotubes obtained in this work are attractive candidate materials for the magnetic and EM wave absorption applications.