Magnetic materials with strong spin-orbit interactions are drawing strong attention as candidates to show unusual magnetism such as quantum spin liquid stabilised by highly frustrated anisotropic Kitaev interactions and further neighbour interactions as well as strong quantum fluctuations by low spin state. Multiferroicity with strong spin-orbit-coupled magnetic ions in the honeycomb lattice is thus attracting a special attention as frustration could be related to the new mechanism in connecting magnetisation and electric polarisations. In this project, we focus on a honeycomb multiferroic candidate with strong magnetoelastic coupling: a buckled honeycomb antiferromagnet Co4Ta2O9 with strong spin-orbit-coupled Co2+ ions. We aim to solve magnetic structure of Co4Ta2O9 to have an insight on the origin of unusually large ME coupling.