Effective anisotropy field variation of magnetite nanoparticles with size reductionJ. M. Vargas, E. Lima, R. D. Zysler, J. G.S. Duque, E. De Biasi and M. KnobelEur. Phys. J. B, 64 2 (2008) 211-218DOI: https://doi.org/10.1140/epjb/e2008-00294-6