Recent studies have demonstrated that YTiO3 exhibits transient ferromagnetism at temperatures nearly three times the thermodynamic Curie temperature TC = 28 K when subjected to all-optical, mode-selective phonon pumping [1]. By manipulating specific phonon modes, it is possible to either enhance and stabilize ferromagnetism or, conversely, reduce the net magnetic moment. This demonstrates that spin-phonon coupling in YTiO3 facilitates the dynamic control of its magnetic properties, although the underlying mechanism remains elusive. In the proposed study, we aim to confirm our hypothesis that the extraordinary sensitivity of the magnetic moment to phonon pumping may arise from a possible compensating magnetic moment on Y due to the hybridization of the Ti 3d-orbitals with the Y 4d-orbitals. We propose to perform a systematic XMCD study at the yttrium L2,3 X-ray absorption edges in La- and Ca-substituted YTiO3 as a function of temperature and applied magnetic field.