Interface and Bulk Charge Localization in Manganite Thin Films

Nuclear magnetic resonance (NMR) is utilized to map the hyperfine fields acting on Mn-55 nuclei of La2/3Sr1/3MnO3 (LSMO) epitaxial thin films. In contrast to early thoughts, we show that phase separation (PS) in LSMO is not restricted to an interface-related dead-layer only a few nm thick. Instead, it propagates much deeper into the films, thus signalling different origins for the PS. These results indicate that both, surfaces and defects contribute to promote distinguishable PS effects. This view has been confirmed by detailed Mn-55 NMR analysis of LSMO films where engineered bulk-like defects have been created by appropriate irradiation by energetic He+ ions. Moreover, from the analysis of the restoring fields sensed by the spins of the Mn-55 nuclei, we infer two sources of magnetic anisotropy. More specifically, a surface magnetic anisotropy -linked to the interfacial dead layer- is predominant for ultrathin samples (t < 10 nm), whereas structural film relaxation, provides a second mechanism for anisotropy. These findings provide guidelines for the growth of electric and magnetic homogeneous manganite films.