Temperature dependence of magnetic properties of La 0.7 Sr 0.3 MnO 3 / SrTiO 3 thin films on silicon substrates

20-nm-thick and 50-nm-thick ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_{3}$ films were grown by molecular-beam epitaxy on Si (001) substrates overlaid by a 20-nm-thick ${\text{SrTiO}}_{3}$ (001) buffer layer. X-ray diffraction and atomic force microscopy studies demonstrate their epitaxial (001) orientation. Their static magnetic properties are investigated as a function of the temperature using a superconducting quantum interference device. Ferromagnetic resonance (FMR) inside a cavity and microstrip ferromagnetic resonance (MS-FMR) are used to study their dynamic properties. The field dependence of the MS-FMR resonance frequency as a function of a perpendicular applied field provides a precise evaluation of the $g$ factor and of the effective demagnetizing field $4\ensuremath{\pi}{M}_{eff}$ at room temperature. The perpendicular uniaxial and the in-plane anisotropies strongly decrease versus temperature. The excellent epitaxial crystallographic orientation due to the ${\text{SrTiO}}_{3}$ buffer gives rise to an observed fourfold symmetry of the in-plane anisotropy which is assumed of magnetocrystalline nature. The large perpendicular uniaxial anisotropy gives rise to an effective demagnetizing field significantly larger than the resulting one from the sole contribution of the saturation magnetization. It is most probably induced by the interfacial strain.