On magnetoconductivity of metallic manganite phases and heterostructures

We use the double exchange (DE) model via degenerate orbitals and tight-binding approximation to study the magnetoconductivity of a canted A-phase of pseudo-cubic manganites. It is argued that the model is applicable in a broad concentration range for manganites with the tolerance factor, t, close to one. As for the substitutional disorder, scattering on random Jahn-Teller distortions of MnO6 octahedra is chosen. We emphasize an intimate correlation between the carrier concentration and resistivity value of metallic manganites. Magnetoresistance as a function of magnetization is calculated for a canted A-phase for both in-plane and out-of-plane current directions. A contact between two manganite phases is considered and structure of the transition region near the contact is discussed. Numerical calculations show charge re-distribution near the contact and a large screening length of the order of five inter-atomic distances. We employed our results to interpret data obtained in recent experiments on La0.4Sr0.6MnO3/La0.55Sr0.45MnO3 superlattices. We also briefly discuss the relative importance of the cooperative Jahn-Teller distortions, double exchange mechanism and super-exchange interactions for the formation of the A-phase at increasing Sr concentrations x>0.45 in LSMO to suggest that the Jahn-Teller contraction of octahedra, c/a<1, plays a prevailing role.