Anomalous thermal properties and local lattice effects in low doped manganites La0.875Ca0.125MnO3 and La0.875Ca0.0625Sr0.0625MnO3

The results of a comparative study of the magnetic, transport and thermal properties of two ferromagnetic La0.875Ca0.125MnO3(LCMO) and La0.875Ca0.0625Sr0.0625MnO3 (LCSMO) samples with the same Mn3+/Mn4+ ratio and identical crystallographic structure have been presented. While LCSMO exhibits magnetic transition accompanied by an insulator to metal transition, no such transition is observed in LCMO. Moreover, unlike LCMO, only in the case of LCSMO, is a sudden drop in the thermoelectric power S( T) along with an enhancement in the value of thermal conductivity.( T) observed below the Curie temperature (T-C). This confirms that not only the Mn3+/ Mn4+ ratio but also local lattice effects and carrier transport play a vital role in determining in the physical properties of these low doped manganite systems.