Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We report the facile and easy synthesis process of iron oxide (Fe3O4) nanoparticles (Fe3O4 NPs) modified surface of carbon nanotubes (CNTs) and their magnetic properties. The partially aligned multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (CNx-MWCNTs) were synthesized through chemical vapor deposition (CVD) method. In next step, synthesized MWCNTs and CNx-MWCNTs were anchored with Fe3O4 NPs using microwave (MW) irradiation. The size of anchored Fe3O4 NPs on surface of Fe@MWCNTs and Fe@CNx-MWCNTs were 5-15 and 5-10 nm, respectively. The investigation results of magnetic properties revealed that the saturation magnetization of Fe@CNx-MWCNTs was improved after N-doping and Fe@CNx-MWCNTs showed superior magnetization behaviour than Fe@MWCNTs. The saturation magnetization value increases from 26.1 to 30.4 emu/g after N-doping. The improved magnetic performance of Fe@CNx-MWCNTs may be due to the induced structural defect on the surfaces which supports Fe3O4 NPs to attach and consequently improves the saturation magnetization. (C) 2016 Elsevier B.V. All rights reserved.69517931801CNPq (Brazil)FAPESP (Brazil)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)