We investigate the effects of post-annealing on a set of identically deposited Sr₂FeMoO₆ (SFMO) thin films. The annealing provides a significant enhancement to ferrimagnetic exchange, evidenced by almost 40 K increase in Curie temperature. The electronic nature of the film surface is our focus of interest. The detailed analysis on oxygen 1s, strontium 3d, molybdenum 3d spectrum along with changes in the carbon contamination show purification from additional phases and significant valence fluctuation. Successful treatment provides films with higher Curie temperature and diminished surface contamination. Annealing therefore provides a possible method of reobtaining a portion of the valuable bulk attributes at interfaces in e.g. spin valve structures.