Phase coexistence in Cr-doped Nd0.5Ca0.5MnO3 compounds

We have performed measurements of dc electrical resistivity rho(T), magnetic susceptibility chi(T), and impedance spectroscopy Z(T, omega) in both single crystals and polycrystalline samples of Nd0.5Ca0.5Mn1-xCrxO3 (0.00less than or equal toxless than or equal to0.07). The pristine compound exhibits a transition to a charge ordered (CO) state at T(CO)similar to250 K. However, no evidence of either metal-insulator (MI) or ferromagnetic (FM) transitions are observed at lower temperatures. The substitution of Mn by Cr partially suppresses the CO transition and induces a FM/MI ordering at lower temperatures T-C=T(MI)similar to140 K, which is essentially Cr independent. Both rho(T) and chi(T) measurements indicate the development of a ferromagnetic (FM) component at low temperatures T<T-MI that gradually increases with increasing Cr content. The ρ(T) and χ(T) data also revealed irreversibility at temperatures T<T-CO suggesting a coexistence of different phases. In addition, the Z(T,omega) curves close to T-MI exhibit a clear relaxation process. The specific capacitances calculated from the Z(T,omega) curves have a percolation-like behavior, characteristic of a metal-insulator transition in samples comprised of two phases. (C) 2003 American Institute of Physics.