We propose to investigate the evolution of the exchange spring (ES) in NdCo5/Fe and SmCo5/Fe with temperature and magnetic fields using polarized neutron reflectometry. The exchange coupling at the interface leads to an ES formed in the soft-magnetic Fe layer when an external field is applied opposite to the initial saturation or at along a hard axis of the material. In NdCo5, a spin-reorientation transition just below room temperature leads to a change of the easy axis from the c-axis to the a-axis. This allows to tune the ES without changing the field or sample orientation. In particular, we will use OFFSPEC to gain deeper insight into off-specular asymmetric spin-flip scattering observed in fields > 0.1 T. The scattering is highly asymmetric due to the Zeeman effect and may indicate a domain formation. However, the origin and field dependence is not clearly understood as a domain form