Low-temperature ferromagnetic resonance in bare and SiO2 coated La0.775Sr0.225MnO3 nanoparticles

La0.775Sr0.225MnO3 nanoparticles were synthesized by sol-gel method with heat treatment at T = 1073 K and covered with silica shells of various thicknesses. Analysis of their experimental ferromagnetic resonance spectra was carried out in the temperature range of 77–290 K. The linewidth of absorption curves change in a nonlinear manner in coated samples in the temperature range of 230 K ≤  T ≤ 290 K. Such changes indicate the appearance of external stresses between nanoparticles due to the difference in the thermal expansion coefficients of the two materials.