Thermodynamic and Electron Diffraction Signatures of Charge and Spin Ordering inLa1−xCaxMnO3

Abstract

The large-magnetoresistance compounds ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ have been studied using specific heat, sound velocity $\left(v\right)$, and electron diffraction. For $0.63\le x\le 0.67$ charge ordering is observed at 260 K and accompanied by a dramatic $(>10\mathrm{}\%)$ 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 $d^4$ 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.