High-pressure phase diagram in the manganites: a two-site model study

The pressure dependence of the Curie temperature T-C in manganites, recently studied over a wide pressure range, is not qualitatively accounted for by the quenching of Jahn-Teller distortions, and suggests the occurrence of a new pressure-activated localizing process. On the basis of several high-pressure experiments, the antiferromagnetic (AF) interaction between the core spins has been suggested as a good candidate for such a localizing mechanism. We present a theoretical calculation of T-C based on a two-site double-exchange model with electron-phonon coupling interaction and direct superexchange (SE) between the t(2g) core spins. We calculate the pressure dependence of T-C and compare it with the experimental phase diagram. Our results describe the experimental behaviour quite well only if a pressure-activated enhancement of the AF-SE interaction is assumed.