Griffiths Phase and Disorder in Perovskite Manganite Oxides La1−xCaxMnO3 and La0.7Sr0.3MnO3

Polycrystalline samples La1−xCaxMnO3 (x=0.17, 0.15, 0.10) and La0.7Sr0.3MnO3 were prepared in order to investigate the Griffiths-like features induced by disorder compared with their counterpart single crystals. The magnetization data exhibit the traditional transition from ferromagnetic phase to paramagnetic phase. From the temperature dependence of inverse susceptibility, it can be testified that the Griffiths-like features still exist in as-prepared Ca doped samples, while non-Griffiths-like features exist in La0.7Sr0.3MnO3. All these samples, however, exhibit the large effective spins resulting from formation of the short-order ferromagnetic clusters. The O K-edge X-ray absorption spectra indicate the Jahn–Teller (J-T) distortions are definitely present due to the J-T ion Mn3+, which indicate that static J-T distortion is not a sufficient condition for the existence of Griffiths phase in Sr-doped system. And, the size of J-T distortion is a little larger in polycrystalline La0.7Sr0.3MnO3 than that in polycrystalline samples La1−xCaxMnO3 (x=0.17, 0.15, 0.10), revealed by X-ray diffraction parameters and extended X-ray fine structure absorption data of Mn K-edge. It also testifies that the disorder in La0.7Sr0.3MnO3 caused by both chemical doping and J-T distortions is lower than that in polycrystalline samples La1−xCaxMnO3, which may be the reason of non-Griffiths-like phase existing in La0.7Sr0.3MnO3 samples.