Thermoelectric effect inLa1−xSrxMnO3

The thermoelectric effect and its systematic variation with doping level ($x$), temperature ($T$), and external magnetic field ($H$) have been investigated for crystals of double-exchange ferromagnets, ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x\mathrm{Mn}{\mathrm{O}}_3$ ($0.15<~x<~0.50$). Large $T$- and $H$-dependent changes of the Seebeck coefficient $S$ are observed around the Curie temperature $T_C$ due to the corresponding changes of resistivity. $S$ changes its sign from positive to negative around the insulator-metal phase boundary ($x=0.20\mathrm{}$) above $T_C$ for the paramagnetic phase, but around $x=0.30\mathrm{}$ in the ferromagnetic metallic state far below $T_C$. A possibly anomalous change of the electronic structure with the spin-polarization is argued on the basis of the magnetothermoelectric data for the moderately doped ($x=0.20-0.30\mathrm{}$) crystals.