As part of a project to develop new electronic materials based on the coupling of electronic and structural properties in new perovskites we have been investigating the properties of S=1/2 Mo5+ containing double perovskites. Sr2YbMoO6 forms a monoclinically distorted double perovskite structure at room temperature, but on cooling below 50 K shows an unusual structural phase transition, forming two monoclinic phases. On cooling further, there is magnetic ordering transition observed in the susceptibility at 24 K, yet no signatures of this are seen in the neutron diffraction. The proposed muSR experiment will allow us investigate the local magnetic behaviour through each of these transitions, giving us an insight into the nature of each of the phases.