Observation of Strain Induced Crystal Field Changes in La0.8MnO3 Single Crystal Manganite Films

We have studied La$_{0.8}$MnO$_{3}$ single crystal manganite films with varying thickness (from 4000 {\AA} to 50 {\AA}) on LaAlO$_{3}$ substrates. We measured the Mn K$_{\beta }$ x-ray emission spectrum, which is sensitive to the crystal field about the Mn sites. Our high-resolution x-ray emission results showed there exists a strong crystal field in manganite films near the substrate due to substrate induced compression of the films. The strong crystal field leads to a partial Mn 3d high spin to low spin transformation. This observation provides a clue to the origin of the reduction in the bulk magnetization in ultrathin manganite films.