Synthesis of novel ZnxCo1−xAl0.5Fe1.46La0.04O4; 0.0≤x≤0.6 nanowires, and optimization of their transport and magnetic properties

Abstract

ZnxCo1−xAl0.5Fe1.46La0.04O4; 0.0≤x≤0.6 nanowires are synthesized for the first time using urea auto-combustion method. X-ray diffraction (XRD) results prove the phase formation, while transmission electron microscope images prove that the flash auto-combustion method is a successful and easy method for obtaining nanowire-bundle filaments in this type of ferrite. At x=0.0, nano-spheres were obtained with average size≈22nm, while the formation of nanowires started at x=0.2, at which nanowire-bundle filaments begin to grow on the surface of these nano spheres with average lengths≈150nm and narrow outer diameters with average value≈22nm. The quantity of nanowires increased with increasing Zn-content substitution to reach its maximum quantity at x=0.4, after which it decreased at x=0.5. This observation accords well with the inversion point that occurs in the lattice parameters at x=0.5. The conduction mechanism in the samples of x=0.0 and x=0.5 reveals the quantum mechanical tunneling, while that in the samples of x=0.2 and x=0.3 reveals overlapping large polaron. The Seebeck coefficient for all the investigated samples takes a +ve sign pointing to a p-type conduction. The sample Zn0.6Co0.4Al0.5Fe1.46La0.04O4 showed paramagnetic behavior, while the sample Zn0.4Co0.6Al0.5Fe1.46La.04O4 showed the largest Curie temperature (TC=790K), the lowest conductivity (σ=0.117×10−3Ω−1cm−1), and resulted in the formation of the maximum quantity of nanowire-bundle filaments which are characterized by their large surface area, that might result in a unique behavior which has never been obtained within traditional bulk materials or normal nano-spheres. One recommends the use of such sample in nanobuilding structures demanding low conductivity and high Curie temperature.