The magnetization vs applied magnetic field curves of Fe \( _{3} \) O \( _{4 } \) measured from vibrating sample magnetometer and the particle size distribution determined from transmission electron micrographs are compared to investigate the influence of magnetic anisotropy and particle size distribution on the magnetization analysis. The sample of Fe \( _{3} \) O \( _{4 } \) nanoparticles is prepared by a chemical method. The structural characterization of the sample reveals that it is a nanocrystalline single phase magnetite system. The transmission electron microscope studies show that the sample has narrow particle size distribution with mean particle size of 12 nm. The magnetic characterization of the sample is measured as a function of temperature and applied magnetic field. The field cooled and zero field cooled curves of Fe \( _{3} \) O \( _{4 } \) nanoparticles are measured in the presence of 250 G applied magnetic field. The bifurcation temperature of the curves is found to be 182 K. The blocking temperature of the system is observed at 154 K from zero field cooled curve. The magnetization curves as a function of applied magnetic field at temperatures of 200, 250, and 300 K are measured (up to \( \pm 10 \) kG). The analysis of magnetization curves is done by fitting these in a mathematical magnetic expression, which takes into account the combined effect of particle size distribution and magnetic anisotropy. The magnetic properties of this system are found to be affected by the presence of the magnetic disordered surface layer on the particles’ surface, which result into the increased interparticle interactions and enhanced surface anisotropy. These observations are discussed in detail.
