RESEARCH PAPER Enhanced magnetic properties of aluminum oxide nanopowder reinforced with carbon nanotubes Frank Zoladz & Steven Rhodes & Dwight Patterson & Warner Cribb & Puskar Chapagain & Dereje Seifu & Valentin Taufour & Saeed Kamali & Suman Neupane Received: 29 March 2020 /Accepted: 28 May 2020 # Springer Nature B.V. 2020 Abstract Magnetic carbon nanotubes (CNTs)/alumina (Al 2 O 3 ) nanocomposites were synthesized by the direct growth of CNTs on alumina by chemical vapor deposi- tion (CVD) process. X-ray diffraction studies show that the crystalline structure of alumina nanoparticles re- mains preserved during the CVD process. Electron mi- croscopy studies reveal the uniform distribution of CNTs within the alumina matrix. CNTs of average diameter 20 nm are spread around alumina particles of size 120 nm. The proportion of CNTs in alumina com- posites is determined to be approximately 10% from the thermogravimetric analysis. CNT-reinforced alumina nanocomposites demonstrate a significant improvement of the magnetic properties as compared with pristine alumina powder. The diamagnetic property of alumina nanopowder is transformed into a strongly pronounced ferromagnetic response upon the incorporation of CNTs. The saturation magnetization increased by ~ 2500%, and a pronounced coercivity of 68 Oe was observed in the nanocomposites. It is suggested that the encapsulation of cobalt inside the CNTs constrains the magnetic moments to result in higher saturation magnetization. Hence, the CNTs/Al 2 O 3 system synthe- sized in this work can be employed to engineer novel ceramic composites with enhanced magnetic properties. Keywords Carbon nanotubes . Alumina . Composites . Coercivity . Field-cooled/zero-field-cooled magnetization . Nanomaterials Introduction Carbon nanotubes (CNTs) have attracted tremendous research interests because they exhibit several outstand- ing physical and chemical properties (Laird et al. 2015; He et al. 2018; Muhulet et al. 2018). For example, CNTs demonstrate tremendously large values of Young’s modulus resulting in superior mechanical strength J Nanopart Res (2020) 22:157 https://doi.org/10.1007/s11051-020-04896-6 F. Zoladz : S. Rhodes : S. Kamali (*) : S. Neupane (*) Department of Physics and Astronomy, Middle Tennessee State University, Murfreesboro, TN, USA e-mail: saeed.kamali@mtsu.edu e-mail: suman.neupane@mtsu.edu D. Patterson Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN, USA W. Cribb Department of Geosciences, Middle Tennessee State University, Murfreesboro, TN, USA P. Chapagain Engineering and Physics Department, Southern Arkansas University, Magnolia, AR, USA D. Seifu Department of Physics, Morgan State University, Baltimore, MD, USA V. Taufour Department of Physics, University of California, Davis, CA, USA S. Kamali Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee Space Institute, Tullahoma, TN, USA