Competitive effects on the high-pressure phase diagram of manganites

Recent infrared absorption measurements performed at different pressures and temperatures on the La0.75Ca0.25MnO3, manganite provided the insulator-to-metal transition temperature T-IM(P), i.e. the P-T phase diagram of the manganite. We report an extended data analysis, by considering in detail pressure and temperature dependence of the observed IR active phonon and of the absorption spectral weights N*. The phonon pressure-dependence, consistently with the P-T phase diagram, indicates the onset of a new localizing interaction above P* = 6-7 GPa. Finally a simple theoretical model will be employed to give a qualitative explanation of the observed high-pressure behavior and to suggest the relevance of the charge-localizing super-exchange magnetic interaction in the very high-pressure regime. Within this framework the asymptotic regime at high pressure is ascribed to the competition between the magnetic super- and double-exchange interactions.