Enhanced surface anisotropy in nickel ferrite nanoparticles - Goya, Gerardo Fabían; Gonçalves, Márcio; Rechenberg, Hercilio Rodolfo; Sousa, M H; Souza, E C; Lara, C F L; Tourinho, F A; Depeyrot, J (International Conference on Magnetic Fluids, 2004)