Magnetoresistance and magnetothermoelectric power of La0.5Pb0.5Mn1-xCrxO3 - art. no. 104428

We report the results of thermoelectric power (TEP) of a Cr doped La0.5Pb0. 5Mn1-xCrxO3 (x=0-0.45) system measured both in the presence and the absence of magnetic field (B=1.5 T). The small field dependence of the Seebeck coe fficient is observed around the metal-semiconductor transition (MST) temper ature (T-p) of the samples. The field dependence of TEP is stronger in the undoped sample. It is noticed from the TEP data that the small polaron hopp ing conduction mechanism is valid for all these samples (for T>T-p). The po laron radius r(p) is found to decrease with increase of magnetic field. Low -temperature (below T-p) field-dependent and field-independent TEP data can be fitted with S=S-0+S3/2T3/2+S4T4 suggesting that the electron-magnon sca ttering strongly affects the low-temperature (ferromagnetic phase) TEP data of the manganites. Activation energy gradually increases with increasing C r concentration both in the presence and the absence of magnetic field. Fie ld-dependent thermopower also indicates the importance of spin fluctuations affecting the phonon scattering, Power factor (S-2/rho) estimated from the Seebeck coefficient (S) And resistivity (rho) (at zero and 1.5 T field) sh owed a minimum around the MST temperature similar to the field-dependent th ermal conductivity data.