Thermodynamic and electron diffraction signatures of charge and spin ordering in La_{1 − x} Ca_xMnO₃

The large-magnetoresistance compounds La_1-xCa_xMnO₃ have been studied using specific heat, sound velocity (v), and electron diffraction. For 0.63 ≤ x ≤ 0.67 charge ordering is observed at 260 K and accompanied by a dramatic (>10%) increase in v. This simultaneous occurrence of electron and lattice ordering features implies extremely strong electron-phonon coupling, known to exist for the octahederally coordinated d⁴ 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.