Ratchet effect of the domain wall by asymmetric magnetostatic potentials Appl. Phys. Lett. 99, 192512 (2011) Crystallization behavior and high temperature magnetic phase transitions of Nb-substituted FeCoSiBCu nanocomposites Appl. Phys. Lett. 99, 192506 (2011) Room temperature magnetoelectric memory cell using stress-mediated magnetoelastic switching in nanostructured multilayers Appl. Phys. Lett. 99, 192507 (2011) Current-induced domain wall motion in permalloy nanowires with a rectangular cross-section J. Appl. Phys. 110, 093913 (2011) Correlation between symmetry-selective transport and spin-dependent resonant tunneling in fully epitaxial Cr/ultrathin-Fe/MgO/Fe(001) magnetic tunnel junctions Appl. Phys. Lett. 99, 182508 (2011) Additional information on J. Appl. Phys. We have systematically studied the magnetic properties of ferrite nanoparticles with 3, 7, and 11 nm of diameter with very narrow grain size distributions. Samples were prepared by the thermal decomposition of Fe͑acac͒ 3 in the presence of surfactants giving nanoparticles covered by oleic acid. High resolution transmission electron microscopy ͑HRTEM͒ images and XRD diffraction patterns confirms that all samples are composed by crystalline nanoparticles with the spinel structure expected for the iron ferrite. ac and dc magnetization measurements, as well in-field Mössbauer spectroscopy, indicate that the magnetic properties of nanoparticles with 11 and 7 nm are close to those expected for a monodomain, presenting large M S ͑close to the magnetite bulk͒. Despite the crystalline structure observed in HRTEM images, the nanoparticles with 3 nm are composed by a magnetically ordered region ͑core͒ and a surface region that presents a different magnetic order and it contains about 66% of Fe atoms. The high saturation and irreversibility fields in the M͑H͒ loops of the particles with 3 nm together with the misalignment at 120 kOe in the in-field Mössbauer spectrum of surface component indicate a high surface anisotropy for the surface atoms, which is not observed for the core. For T Ͻ 10 K, we observe an increase in the susceptibility and of the magnetization for former sample, indicating that surface moments tend to align with applied field increasing the magnetic core size.