Magnetothermopower in La0.67Ca0.33MnO3 thin films

Abstract

We have measured the thermopower S(T,H) and resistivity ρ(T,H) of laser ablated La0.67Ca0.33MnO3 films, as a function of temperature and external magnetic field. On heating, a metal–insulator transition occurs at temperatures below the resistivity peak, observed via a jump between a low T regime, where S∝T, and a high T regime, where S∝1/T. An applied magnetic field shifts the transition in a postannealed sample to higher temperatures, causing a giant magnetothermopower effect 100×(S8T−S0T)/S8T=−1400%. Both S(T) and ρ(T) are activated at high temperatures, but with significantly different activation energies. We interpret this as an evidence of small polarons at high temperatures.

139Laspectrum and spin-lattice relaxation measurements ofLa2/3Sakaie1, Slichter2, Lin3 et al. 1999Phys. Rev. BSelf Cite26230View full textAdd to dashboardCite

“…A number of experiments detect the presence of small magnetic polarons in the manganites [3,15,16]. Associated with the small magnetic polarons are inhomogeneous magnetic fields which could affect the spectrum shape.…”

Low-temperature electrical transport and double exchange inLa0.67(Pb,Ca<

“…This presumably arises from the onset of magnon scattering which, being a spin flip process, must involve the minority spin band, and which therefore has a different dependence on energy near E F . We note that the peak in the low temperature thermopower that is regularly seen in thin-film samples [19] is absent here, and is therefore not intrinsic to these materials.…”

“…Our data cannot be explained by electron-electron scattering as proposed in previous reports. [19,8,9] While oversimplified, our extension of the standard calculation of one-magnon resistivity to account for spin-split bands gives a qualitative account of the half-metallic suppression of spin-wave scattering at low temperatures. The onset of significant magnon-mediated scattering near 30 K is also reflected in a change in both the temperature and field dependence of the thermopower.…”

Large magnetothermopower and Fermi surface reconstruction inSb2Te2Se

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