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 (La_1-xY_x)_x2/3Ca_1/3MnO₃ (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 ΔH_pp anomalously increases with cooling for the temperature range of T_CG. 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.