Magnetic behavior of nanofilms prepared by assembling different Co ferrite nanoparticles

We study the magnetic characteristics of nanofilms composed of CoFe2O4 nanoparticles synthesized using thermal decomposition (TD) and self-combustion (SC) methods, assembled on glass substrates using the Langmuir-Blodgett technique. Despite both synthesis methods render crystalline Co ferrite nanoparticles, the differences in particle size and saturation magnetization are notable; however, both nanofilms reveal a ferrimagnetic behavior and display a significant surface contribution to the net magnetization at temperatures below 50 K. This effect is attributed to the nanoparticles' surface spins misaligning with the spins of the ordered core and freezing into a disordered structure. Effective anisotropy Keff values were determined, obtaining similar values to the bulk material (Keff ~2x105 J/m3) for the nanofilm made of TD nanoparticles, while the nanofilm prepared with SC nanoparticles presents an enhanced value (Keff=5x105 J/m3). The temperature-dependent saturation magnetization curves were fitted with the modified Bloch’s law and an additional term that corresponds to the frozen spins.