Phase competition in L0.5A0.5MnO3 perovskites -: art. no. 174432

Single crystals of the systems Pr-0.5(Ca1-xSrx)(0.5)MnO3, (Pr1-yYy)(0.5)(Ca1-xSrx)(0.5)MnO3, and Sm0.5Sr0.5MnO3 were grown to provide a series of samples with fixed ratio Mn(III)/Mn(IV)=1 having geometric tolerance factors that span the transition from localized to itinerant electronic behavior of the MnO3 array. A unique ferromagnetic phase appears at the critical tolerance factor t(c)=0.975 that separates charge ordering and localized-electron behavior for t<t(c) from itinerant or molecular-orbital behavior for t>t(c). This ferromagnetic phase, which has to be distinguished from the ferromagnetic metallic phase stabilized at tolerance factors t>t(c), separates two distinguishable type-CE antiferromagnetic phases that are metamagnetic. Measurements of the transport properties under hydrostatic pressure were carried out on a composition t a little below t(c) in order to compare the effects of chemical vs. hydrostatic pressure on the phases that compete with one another near t=t(c).