Magnetic properties of maghemite nanoparticles in a polyvinylpyridine matrix

Magnetic measurements have been carried out on nanocomposites consisting of individual maghemite (γ-Fe₂O₃) particles distributed throughout a polyvinylpyridine matrix with a range of particle sizes and concentrations. Magnetic measurements and particle size measurements have been compared to investigate particle size effects upon magnetic properties. Magnetisation increases slowly with increasing iron content up to approximately 18%, at which point the increase becomes sharper. Magnetic moment, as derived from a modified Langevin equation, is found to be less than the value expected from the particle, indicating possible surface effects. Blocking temperatures have been observed to increase with increasing iron concentration. Assuming no significant particle interactions it is possible to consider the effective anisotropy of individual particles. Effective anisotropy has been observed to increase with decreasing particle size, implying an increase in contribution from surface effects, and increases with the presence of rod shaped particles, implying a contribution from shape anisotropy.