Magnetic localization in mixed-valence manganites

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 s51/2 to the t2g ion core with S 53/2. 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(r/r`) 5@T0$12(M /MS) %/T#, 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. @S0163-1829~97!04513-X#