Epitaxial thin films of La0.7Sr0.3MnO3 have been grown by pulsed laser deposition1 onto Si substrates that were buffered with Bi4Ti3O12 and yttrium-stabilized zirconia. They appear to have excellent structural properties as seen by x-ray diffraction and Rutherford backscattering. We will report spin wave resonance (SWR) and electron paramagnetic resonance (EPR) experiments at 10 GHz for 280≪T≪370 K. We observe drastic changes in the spectra consequent upon small variations in temperature: (i) At 295 K, the linewidth of the first spin wave mode is only 15 Oe (the narrowest ever observed in a manganite), and the field positions Hn of the SWR follow the simple n2 dependence expected of a uniform film, n being the mode number.2 (ii) Below 280 K, the SWR spectra developed other structures, and the resonance positoins do not follow any simple model. (iii) When T is raised to about 300 K, Hn assumes a linear dependence on n, suggesting that the film magnetization has developed a parabolic spatial variation. (iv) Near 350 K, the linewidth effectively diverges. (v) At 370 K, an EPR line with a width of only 170 Oe appears. As shown previously,3 a peak in the linewidth near the Curie temperature TC can arise from a distribution of TC values. However, in the present film, the line essentially loses it integrity near TC as if the magnetic network were splitting into several substructures. The recovery in the paramagnetic state, one can imagine, happens because the magnetic phase is liquidlike and, thereby, - homogeneous. The present observations dramatically demonstrate that to produce thin films of manganites that have desirable properties over a wide T interval, it is essential to ensure a lattice match that is not upset by T variation. ©1997 American Institute of Physics.