Nanostructured Pure and Substituted Cobalt Ferrites: Fabrication by Electrospinning and Study of Their Magnetic Properties

Abstract CoFe 2 O 4 , Co 1-x (Cu, Ni and Zn) x Fe 2 O 4 , and Co 1-x Gd x Fe 2 O 4+δ nanostructures are successfully obtained, via electrospinning technique, using metal nitrates as source of metallic ions (M) and polyvinylpyrrolidone (PVP) as polymeric carrier. FTIR spectra of the as-spun fibers indicate the presence of both, PVP and M ions, interacting through amide-M coordination bonds. Thermogravimetric analyses of the as-spun fibers show that 400 °C is the temperature at which samples lose the maximum amount of weight. After thermal treatments at 300, 600, 800, and 900 °C for 2 hours black powders were obtained. Their XRD patterns show the presence of a pure crystalline spinel-type phase. Fiber morphology was corroborated, for as-electrospun and fired samples at 600 °C (for 2 h), by SEM. Vibrating sample magnetometry (VSM) measurements show the characteristic ferrimagnetic behavior and, saturation magnetization and coercivity, values tailored by substitution of cobalt ions. TEM and HRTEM micrographs of samples treated at 600 °C for 2 h corroborate the presence of nanostructured particles of a spinel phase.