Pristine carbon nanotubes (CNTs) and nickel-filled CNTs (Ni-filled CNTs) were synthesized by chemical vapor deposition using lanthanum nickel alloy (LaNi5) particles as a both catalyst and source for the Ni-filling. Pristine CNTs and Ni-filled CNTs were formed without and with catalyst oxidation of LaNi5 alloy, respectively. Transmission electron microscopy analysis clearly illustrated that the formation of Ni-filling during the growth of CNTs was due to the catalyst oxidation. X-ray diffraction and selected area electron diffraction analysis demonstrated that the encapsulated Ni exists as a single crystal face centered cubic structure. Compared with the pristine CNTs, the first order and second order Raman spectra of Ni-filled CNTs showed a disorder induced D band, an increased I-D/I-G ratio, and a decreased I-G'/I-G ratio. The magnetic properties of the Ni-filled CNTs were studied by vibrating sample magnetometer at room temperature. Coercivity value of Ni-filled CNTs reached the maximum at 445.87 Oe, which is significantly larger than that of the bulk Ni at room temperature. The Ni-filling process through the catalyst oxidation is explained using the "surface segregation" mechanism. In addition, we have suggested the possible growth model involved in their formation. (C) 2014 Elsevier B.V. All rights reserved.