Effect of Structural Characteristics on Magnetic Behavior of Highly-Pure NiFe2O4 Nanoparticles

In this work, the sol-gel and dc reactive magnetron sputtering techniques were used to prepare nickel ferrite nanoparticles (NiFe2O4 NPs). In the sol-gel method, citric acid was used as a fuel to decompose metal complexes at a low temperature. The nanoparticle size of NiFe2O4 structures prepared by the dc reactive magnetron sputtering was smaller (∼31 nm) than those prepared by the sol-gel method (∼47 nm). The effects of the structural characteristics on the magnetic behavior of these nanoparticles were introduced by the vibrating sample magnetometer (VSM) measurements performed at room temperature. It was found that the nanoparticles synthesized by the sol-gel process exhibit ferromagnetic properties with a saturation magnetization 30.02 emu/g, while those synthesized by dc reactive magnetron sputtering exhibit superparamagnetic properties with a saturation magnetization of 27.05 emu/g. This difference is attributed to the quantum size effect resulted from the decrease in nanoparticle size.