PHENOMENOLOGICAL MODEL FOR GIANT MAGNETORESISTANCE IN LANTHANUM MANGANITE

The electrical conductivity of doped lanthanum manganite exhibits acti vated semiconducting behavior at high temperatures, and a transition t o metallic behavior at low temperatures in the ferromagnetic state. Th ese two regimes are combined in a new phenomenological equation for th e conductivity that uses a mean-field magnetization and physically rea sonable fitting parameters. This allows us to account quantitatively f or reports of giant negative magnetoresistance in single crystals and thin films. We present new data on sputtered epitaxial thin films of L a1-xCaxMnO3, and analyze other recent reports in the literature. The p hysical basis for such an expression is discussed. (C) 1996 American I nstitute of Physics.