Temperature dependent magnetic properties of CoFe 2 O 4 /CTAB nanocomposite synthesized by sol–gel auto-combustion technique

Abstract

A CoFe 2 O 4 /cetyl trimethylammonium bromide (CTAB) nanocomposite has been fabricated by a sol–gel auto-combustion method. Characterization of the material revealed the composition of the crystalline phase as CoFe 2 O 4 while FT-IR confirmed the presence of CTAB on the nanoparticles. From X-ray line profile fitting, average crystallite size was estimated to be 22±6 nm. SEM analysis showed a porous sheet-like morphology with internal nanosize grains of about 30 nm. The room temperature coercive field ( H c ) of the CoFe 2 O 4 /CTAB nanocomposite was found to be 1045 Oe which is close to the previously reported room temperature values for bulk CoFe 2 O 4 . The H c was observed to decrease almost linearly with the square root of the temperature (√T) according to Kneller's law . From the linear fit of H c versus √T, the zero-temperature coercivity ( H c 0 ) and superparamagnetic blocking temperature ( T B ) of the CoFe 2 O 4 /CTAB nanocomposite were found to be ∼9.1 kOe and ∼425 K, respectively. The remanence magnetization ( M r ), the reduced remanent magnetization ( M r / M s ), and the effective magnetic anisotropy ( K eff ) decrease with increasing temperature. The M r / M s value of 0.6 at 10 K higher than the theoretical value of 0.5 for non-interacting single domain particles with the easy axis randomly oriented suggests the CoFe 2 O 4 /CTAB nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.