Microstructural and magnetic properties of (La_0.7Sr _0.3MnO₃)_0.7:(Mn₃O₄) _0.3 nanocomposite thin films

Epitaxial (La_0.7Sr_0.3MnO₃) _0.7:(Mn₃O₄)_0.3 (LSMO:Mn ₃O₄) nanocomposite thin films were grown on SrTiO ₃ (001) substrate by a pulsed laser deposition technique. The nanocomposite structures vary from triangular domains, to vertically aligned columns, and finally to smaller spherical domains as the deposition frequency varies from 1, 5, to 10 Hz, respectively. The strain in LSMO is systematically tuned, but that of the Mn₃O₄ phase is relatively stable as the deposition frequency increases. The tunable strain is found directly related to the different domain and grain boundary (GB) structures. Physical properties including saturation magnetization, Curie temperature (T _C), magnetoresistance and metal-insulator transition temperature (T_MI), all show systematic trends as the deposition frequency varies. This study reveals that the domain/GBs tunability achieved in nanocomposite thin films can affect the lattice strain and further tune their ferromagnetic properties.