Thermodynamic and electron diffraction signatures of charge and spin ordering in La1-xCaxMnO3

The large-magnetoresistance compounds La1-xCaxMnO3 have been studied using specific heat, sound velocity (upsilon), and electron diffraction. For 0.63 less than or equal to x less than or equal to 0.67 charge ordering is observed at 260 K and accompanied by a dramatic (>10%) increase in upsilon. This simultaneous occurrence of electron and lattice ordering features implies extremely strong electron-phonon coupling, known to exist for the octahederally coordinated d(4) ion and originating in the Jahn-Teller effect. A dynamic manifestation of this Jahn-Teller coupling has been suggested by Millis et al. as the origin for colossal magnetoresistance.