Single crystalline FeCo nanoparticles with tunable size and shape were prepared by co-decomposing two metal-amide precursors under mild conditions. The nature of the ligands introduced in this organometallic synthesis drastically affects the reactivity of the precursors and thus the chemical distribution within the nanoparticles. The presence of the B2 short-range order was evidenced in FeCo nanoparticles prepared in presence of HDAHCl ligands, combining 57 Fe Mössbauer, zero field 59 Co Ferromagnetic Nuclear Resonance (FNR) and X-ray diffraction studies. This is the first time that the B2 structure is directly formed during synthesis without the need of any annealing step. The as-prepared nanoparticles exhibit magnetic properties comparable with the ones of the bulk (Ms = 226 Am².kg-1). Composite magnetic materials prepared from these FeCo nanoparticles led to a successful