Low-Temperature Permittivity of Insulating Perovskite Manganites

TL;DR

This study investigates the low-temperature dielectric properties of insulating perovskite manganites, revealing charge-carrier dynamics, impurity levels, and a notably high dielectric constant near specific magnetic states.

Contribution

It provides detailed measurements of permittivity and conductivity across various compositions, introducing a simple impurity model and identifying a large dielectric constant in a particular magnetic phase.

Findings

Charge-carrier hopping peaks observed in permittivity.

Effective mass estimated at ~3 for Mn(4+) compounds.

Large dielectric constant (~100) near La(0.2)Ca(0.8)MnO(3).

Abstract

Measurements of the low-frequency (f<=100 kHz) permittivity and conductivity at T<= 150 K are reported for La(1-x)Ca(x)MnO(3) (0<=x<=1) and Ca(1-y)Sr(y)MnO(3) (0<=y<=0.75) having antiferromagnetic, insulating ground states covering a broad range of Mn valencies from Mn(3+) to Mn(4+). Static dielectric constants are determined from the low-T limiting behavior. With increasing T, relaxation peaks associated with charge-carrier hopping are observed in the real part of the permittivities and analyzed to determine dopant binding energies. The data are consistent with a simple model of hydrogenic impurity levels and imply effective masses m*/m_e~3 for the Mn(4+) compounds. Particularly interesting is a large dielectric constant (~100) associated with the C-type antiferromagnetic state near the composition La(0.2)Ca(0.8)MnO(3).