Griffiths phases vs magnetic polarons in the lightly doped La1−xSrxMno3

The nature of the ferromagnetic (FM)-paramagnetic (PM) transition in perovskite-doped manganites is the subject of considerable discussions. There is no general consensus about the microscopic physics of stable FM clusters within PM matrix for the temperature range around Curie temperature. Our measurements of electron-spin resonance and magnetic susceptibility in the system La1-xSrxMnO3 (0.07≤x≤0.16) reveal a novel triangular Griffith's-phase regime, which arises as a result of the strong quenching of the randomly diluted locations of the FM bonds in the cooperatively Jahn-Teller-distorted orthorhombic structure. However, the Griffith's singularities disappear for x>0.16. In this case, an applicability of description based on magnetic polarons coupled on lattice distortions will be discussed. © 2006 Elsevier B.V. All rights reserved.