Introduction.- Iron based superconductors.- Neutron scattering.- Phase diagram and incommensurate antiferromagnetic order of BaFe
2-xNi
xAs
2.- Origin of the incommensurate magnetic order in BaFe
2-xNi
xAs
2.- Nematic spin correlations in detwinned BaFe
2-xNi
xAs2.- Magnetic excitations in overdoped BaFe
2-xNi
xAs
2.- Summary and outlook.- References.- Publications.- Resume.- Acknowledgements.