Doping Dependence of Polaron Hopping Energies in La(1-x)Ca(x)MnO(3) (0<= x<= 0.15)

TL;DR

This study investigates how doping levels affect polaron hopping energies in La(1-x)Ca(x)MnO(3), revealing insights into charge transport and magnetic states near the insulator-metal transition.

Contribution

It provides experimental measurements linking dielectric and resistivity data to polaron hopping energies across different doping levels.

Findings

Polaron hopping energies vary with doping.

Charge-carrier hopping activation energies match resistivity data.

Insulator-metal transition is hindered by ferromagnetic insulating state.

Abstract

Measurements of the low-frequency (f<= 100 kHz) permittivity at T<= 160 K and dc resistivity (T<= 430 K) are reported for La(1-x)Ca(x)MnO(3) (0<= x<= 0.15). Static dielectric constants are determined from the low-T limiting behavior of the permittivity. The estimated polarizability for bound holes ~ 10^{-22} cm^{-3} implies a radius comparable to the interatomic spacing, consistent with the small polaron picture established from prior transport studies near room temperature and above on nearby compositions. Relaxation peaks in the dielectric loss associated with charge-carrier hopping yield activation energies in good agreement with low-T hopping energies determined from variable-range hopping fits of the dc resistivity. The doping dependence of these energies suggests that the orthorhombic, canted antiferromagnetic ground state tends toward an insulator-metal transition that is not realized due to the formation of the ferromagnetic insulating state near Mn(4+) concentration ~ 0.13.