Control of magnetism purely with electric field is a key goal of spintronics as it offers low power alternatives to current computer memory devices. The piezomagnetic effect (PME), the linear dependence of magnetisation with strain, offers a novel method to achieve this with significant advantages over current magnetostriction-based devices as it allows complete reversal of the magnetisation. Recently, we have predicted a giant PME in Mn3NiN films. To investigate this we have successfully grown thin films of Mn3NiN on various substrates and found strain induced magnetism in excellent agreement with theory. However, in order to confirm that these originate from the PME we need to determine the magnetic structure. Using the high flux WISH diffractometer we plan to determine the magnetic structure of our thin films and thereby confirm the origin of the strain dependent magnetism.