Pressure dependence of the MI-transition temperature under competing double exchange-superexchange interactions close to CDO afm insulating states

The pressure derivative of the order-order transition T1 and the order-disorder transition at small Tc is calculated using a magnetostriction and polaron extended deGennes model in the low x-doped region. According to this model, in the case where there is a semiconducting gap there is no direct pressure dependence of the transition lines but only an indirect one which is connected with the pressure dependence of the transfer integral, even if we have polaronic states. In the case where T1 and the metal-insulator transition Tmi split, there is a direct (quadratic) dependence which is based on a static (polaron) susceptibility of the insulating band edge electronic-phononic states. Pressure experiments on manganite compounds are shown which are consistent with the predictions of the model in detail, e.g. a correlation between dTmi/dp shifts and resistivity changes.