Magnetic localization in mixed-valence manganites

Abstract

The metal-insulator transition is mixed-valence manganites of the (La0.7Ca0.3)MnO3 type is ascribed to a modification of the spin-dependent potential JHs?S associated with the onset of magnetic order at TC. Here JH is the on-site Hund's-rule exchange coupling of an eg electron with s=1/2 to the t2g ion core with S=3/2. Above TC, the eg electrons are localized by the random spin-dependent potential and conduction is by variable-range hopping. Over the whole temperature range, the resistivity varies as ln(?/??)=[T0{1-(M/MS)2}/T]1/4, where M/MS is the reduced magnetization. The temperature and field dependence of the resistivity deduced from the molecular-field theory of the magnetization reproduces the experimental data over a wide range of temperature and field.