We have discovered a new quaternary intermetallic phase MnCoGe1/3As2/3 (hereafter denoted as MCGA), “hidden” between ternary compositions MnCoGe (MCG) and MnCoAs (MCA). Remarkably, MCGA reveals a different structure type in comparison to MCG and MCA and drastically different magnetic properties relative to the ternary parent phases. We propose to use X-ray magnetic circular dichroism (XMCD) technique to complement the results of our recent neutron diffraction studies to elucidate conclusively the magnetic structure of MCGA, which exhibits at least three distinct magnetically ordered regimes as a function of temperature. The aim of this project is to measure XMCD spectra at the K-edges of Mn and Co to determine the values and orientation of the magnetic moments and to establish if the ordering is ferromagnetic (FM) or ferrimagnetic (FiM) in nature. We will also perform XMCD at the K-edges of Ge and As to elucidate the role of these elements in the magnetic exchange interactions.