Evidence of the griffiths phase in doped manganites studied by electron paramagnetic resonance measurements

A systematic investigation of electron paramagnetic resonance above the Curie temperature T-C is performed on polycrystalline (La1-x Y-x)(2/3)Ca1/3MnO3 (x = 0, 0.15 and 0.2) samples. The results indicate anomalous paramagnetic behaviour below a temperature T-G and, the anomalous extent increases with cooling from T-G. Especially, the resonance linewidth DeltaH(pp) anomalously increases with cooling for the temperature range of T-C < T < T-G. The experimental observation is discussed within the framework of the Griffiths theory that predicts the existence of ferromagnetic clusters above T-C. We explain the observed anomalous paramagnetic behaviour to be due to the magnetic heterogeneity caused by the ferromagnetic clusters which appear in the Griffiths phase.