Evolution of the inter-layer coupling in bilayered manganites revealed by ferromagnetic resonance spectra

Ferromagnetic resonance has been used to investigate the inter-layer coupling in a bilayered manganite La2-2xSr1+2xMn2O7 (x = 0.38) single crystal. The coexistence of a ferromagnetic resonance line and a paramagnetic resonance line was observed over a broad temperature range. Antiferromagnetic coupling between the adjacent MnO2 bilayers can be identified from the observation of an optical mode in the resonance spectra. Analysis of the temperature dependence of the resonance field and intensity reveals the evolution of the inter-layer coupling as a function of temperature. Our study suggests that ferromagnetic resonance provides a useful method for investigating the inter-layer coupling in bilayered manganites.