Adiabatic polaron hopping conduction and Griffiths phase in electron-doped Ca0.85Dy0.15MnO3

Abstract

We have studied temperature and magnetic field depended resistivity and magnetization of electron-doped polycrystalline Ca0.85Dy0.15MnO3. The resistivity ρ(T) exhibits semiconducting behavior down to 5 K even on application of magnetic field. The conduction mechanism has been described through hopping model: small polaron hopping (SPH) above 118 K (144 K) and variable range hopping (VRH) below 40 K (56 K) for H = 0T (for 10T). A parallel combination of SPH and VRH has been considered to depict ρ(T) between 40 K < T < 118 K for H = 0T. Magnetization study shows the compound undergoes paramagnetic to ferromagnetic second order phase transition. The non-linear behavior of temperature dependent inverse susceptibility above Currie temperature has been interpreted as the formation of a Griffiths singularities arising due to the presence of magnetic ordered cluster within the paramagnetic matrix. Origin of the observed Griffiths phase has been correlated with the lattice strain at grain boundary.