Magnetic nanoparticles are increasingly used in biomedical applications such as drug-delivery, gene delivery, hyperthermia, or contrast agents for MRI. Magnetite (Fe3O4) nanoparticles are good candidates for these applications due to their non-toxicity and long-life in the bloodstream. Here we show inter-particle magnetic correlations probed at the nanoscale via x-ray resonant magnetic scattering (XRMS). We show the dependence on particle size, varying from 5 to 11 nm, suggesting an enhancement of magnetic couplings for bigger particles. Additionally, we show a model based on chains of nanoparticles. The data fitting suggests ferromagnetic ordering when an external magnetic field is applied, but the emergence of antiferromagnetic ordering at remanence. Additionally we will present photon correlation data that show the dynamics of fluctuation throughout the superparamagnetic blocking transition.