Ferromagnetic resonance studies of nanocrystalline La0.6Pb0.4MnO3 thin films

Systematic magnetic field dependent microwave absorption measurements have been performed on nanocrystalline La0.6Pb0.4MnO3 (LPMO) thin films over a temperature range of 77-300 K. In addition to a regular ferromagnetic resonance (FMR) signal below the Curie temperature of 230 K, we have observed a second FMR line at temperatures < or = 170 K, which is accompanied by a nonresonant microwave absorption signal centered at zero magnetic field. The two components of FMR lines are identified to originate from bulk and surface magnetic orderings of the LPMO nanocrystallites. The temperature dependence of the linewidth (F) revealed that the bulk of the crystallites contain chemical inhomogeneities, while the surface has a magnetic spin glass character. The hysteresis of the nonresonant absorption signal in LPMO films is found to differ from those of superconductors and, to originate due to magneto-induced microwave conductivity of surface spin glass.