Antiferromagnets with triangular spin arrangements attract attention due to the presence of non-trivial spin dependent phenomena. We have grown high quality antiferromagnetic Mn3GaN epitaxial thin films with an anti-perovskite crystalline structure, in which we have observed an unconventional spin-Hall effect. Our theory calculations indicate that such effects depend critically on the type of 120 degree spin configuration, however, the magnetic structure for thin film Mn3GaN is unknown. Our preliminary experiment on WISH confirmed the existence of a 120 degree magnetic structure, but we were unable to determine the specific magnetic symmetry due to the limited beam time and small sample size. Here, we propose more neutron diffraction experiments on WISH to distinguish between all possible magnetic structures. This data would fill the gap between our theory and experiment.