Magnetoresistance and magnetothermoelectric power ofLa0.5Pb0.5Mn

Abstract

We report the results of thermoelectric power ͑TEP͒ of a Cr doped La 0.5 Pb 0.5 Mn 1Ϫx Cr x O 3 (xϭ0 -0.45) system measured both in the presence and the absence of magnetic field (Bϭ1.5 T). The small field dependence of the Seebeck coefficient is observed around the metal-semiconductor transition ͑MST͒ temperature (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 hopping conduction mechanism is valid for all these samples ͑for TϾT p ). The polaron radius r p is found to decrease with increase of magnetic field. Low-temperature ͑below T p ) fielddependent and field-independent TEP data can be fitted with SϭS 0 ϩS 3/2 T 3/2 ϩS 4 T 4 suggesting that the electron-magnon scattering strongly affects the low-temperature ͑ferromagnetic phase͒ TEP data of the manganites. Activation energy gradually increases with increasing Cr concentration both in the presence and the absence of magnetic field. Field-dependent thermopower also indicates the importance of spin fluctuations affecting the phonon scattering. Power factor (S 2 /) estimated from the Seebeck coefficient ͑S͒ and resistivity () ͑at zero and 1.5 T field͒ showed a minimum around the MST temperature similar to the field-dependent thermal conductivity data.

Magnetotransport, thermoelectric power, thermal conductivity and specific heat of Pr2/3Sr1/3MnO3 manganite

“…To verify the above argument we have also fitted the measured TEP data in the metallic region using the following relation: 27,28 …”

“…As the magnon drag effect is approximately proportional to the magnon specific heat, one expects a T 3/2 contribution in S for the FM system. 27,28 We have fitted our temperature dependent S͑T͒ data to the Eq. ͑5͒ and the representative fitting curve is shown in Fig.…”

“…The fitting parameters given in Table I are in good accord with the reported data. 27,28 It is clear that S 3/2 is nearly five orders of magnitude larger than S 4 , implying the second term in Eq. ͑5͒ dominates the transport mechanism in FM region below T C .…”

Structural, Morphological, Magneto-Transport and Thermal Properties of Antimony Substituted (La,Pr)2/3Ba1/3Mn1-xSbxO3 Perovskite Manganites

“…S 0 has no physical origin but inserted to account for the low temperature data, S 3/2 T 3/2 is attributed to single magnon scattering process 68,70 . The term S 4 T 4 dominant in high temperature region near T C , is thought to arise from spin wave fluctuation in the FM phase 68,70 . Figure 12 shows the fitting of Eq.…”

“…Similar to ρ(T) data, several factors, such as impurity, complicated band structure, electronelectron, electron-magnon scattering etc also affect S(T) data in the FM metallic regime. S(T) data in this intermediate temperature FM metallic region has been analyzed by the following relation 68,69 :…”