Interference of coexisting para- and ferromagnetic phases in partially crystallized films of doped manganites

Electron spin resonance spectra have been studied in partially crystallized films of La1−x Nax MnO3 (x = 0.16) in the vicinity of the para- to ferromagnetic transition. The objects of investigation were obtained by magnetron sputtering on polycrystalline Al2O3 substrates held at different temperatures. It is shown that, in a regime where the paramagnetic and ferromagnetic phases coexist, the resonance conditions for one phase strongly depend on the parameters of the other phase. As a result, the resonance field of the paramagnetic phase becomes dependent on the shape of the sample, the saturation magnetization and the fraction of the ferromagnetic phase. A simple model is developed to predict the character of the changes in the resonance field of the paramagnetic phase upon the nucleation of the ferromagnetic phase.