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

The pressure dependence of the Curie temperature TC 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 TC based on a two-site double-exchange model with electron–phonon coupling interaction and direct superexchange (SE) between the t2g core spins. We calculate the pressure dependence of TC 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.