Multiferroic materials - those which exhibit spontaneous and switchable electrical and magnetic polarizations - have a wide range of applications. However preparing new magnetoelectric materials is challenging because ferroelectric and ferromagnetic properties are contraindicated. We have been working of a strategy of introducing magnetic behaviour to existing ferroelectric materials via topochemical cation exchange. Specifically, we are exploring the cation exchange chemistry of polar Dion-Jacobson and Ruddlesden-Popper oxide and oxynitride phases to see if we can induce ferromagnetic behaviour whilst retaining the existing ferroelectric behaviour. We propose to collect neutron powder diffraction data at 5 K from these exchanged phases, so we can determine their magnetically ordered structures to look for magnetoelectric coupling.