Interparticle interaction and size effect in polymer coated magnetite nanoparticles

Magnetization and Mössbauer studies have been performed on the polymer coated magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in the temperature dependence of magnetization ( T M ) is found to be inconsistent with the particle size ( D TEM ). The effective magnetic anisotropy ( K an ) is found to increase with the decrease of D TEM , which is attributed to the increase of surface anisotropy. The absence of coercivity and remanence of magnetization noticed well above T M indicate superparamagnetic behaviour, which has also been observed in the temperature dependent Mössbauer results. The temperature dependence of hyperfine field is found to follow a similar dependence to saturation magnetization for bulk magnetite.