Low spin to high spin phase transition in ultrathin film of La0.7Sr0.3MnO3/SrTiO3

Ultrathin films of manganites often exhibit dramatically different physical properties with respect to the thicker films and the constituent bulk material. Here, we have studied the spin structure of La0.7Sr0.3MnO3 (LSMO) untrathin films grown on SrTiO3 (001) substrate, which remains unresolved till date. Combing results from thickness-dependent magneto-optical Kerr effect and scanning tunneling spectroscopy measurements, we have obtained a full phase diagram of the spin structure of the LSMO ultrathin films. Specifically, the LSMO films are in a low-spin magnetic phase from 4 unit cells to 7 unit cells. Above 9 unit cells , the whole films transform into ferromagnetic metallic state. At the critical thickness of 8 unit cell, the film exhibits an interesting surface spin state that mediates the low-spin to high-spin transition.