FMR study of carbon nanotubes filled with Fe3O4 nanoparticles

•Synthesis of CNTs inside of alumina membrane and filling it with Fe3O4 particles.•X-ray diffraction and electron microscopy study of the samples.•Magnetic properties of the samples studied by FMR.•Filling factor has been determined from the angular dependences of FMR.•Resulted magnetic CNTs are attractive for production of magnetic nanofluids.

Ordered arrays of carbon nanotubes were produced using a non-catalytic chemical vapour deposition. The multiwall nanotubes with an inner diameter of 120 nm were grown inside porous alumina templates and then filled with a magnetic colloid of 7.5 nm Fe3O4 particles. X-ray diffraction, electron microscopy and ferromagnetic resonance (FMR) were used to characterize structural and magnetic properties of the grown samples. To estimate the filling factor from the angular dependence of the FMR resonance field, we have derived an effective demagnetization factor for our system using the formalism proposed by Skomsky and Dubowik. Angular dependence of the FMR line width allows one to conclude about the non-uniform filling, while temperature dependent measurements reflect typical features of a superparamagnetic resonance.