Interacting networks and spin polarization in (Dy, Ca)MnO3

Solid solutions of Dy1-xCaxMnO3 (0.00 less than or equal to x less than or equal to 0.60) were prepared by solid state reaction of oxides and carbonates. Sintered bodies were obtained by firing between 1250 and 1450 degreesC. All compositions, including DyMnO3, crystallize in a perovskite structure of O'-type orthorhombic symmetry and space group Pbnm. Increase of Ca2+ content leads to a monotonic decrease of the orthorhombicity factor b/a. Electrical measurements show a semiconducting behavior for all compositions. The room temperature conductivity increases with Ca content, attaining relatively high values at x = 0.60 and a correlative very low value of the activation energy. Thermally-activated small-polaron hopping mechanism controls the conductivity. Antiferromagnetic interactions between Dy spins are observed at T-N = 9.5 K. DyMnO3 behaves as a metamagnetic-like system, with no remanent magnetization at zero field. ZFC/FC cycles and the thermal evolution of the remanent magnetization of the Dy1-xCaxMnO3 solid solution show the presence of two interacting magnetic networks: a Dy sublattice, with a Curie-Weiss thermal dependence above T-N, aligned antiparallel to the ferromagnetically ordered (T-c = 80 K) Mn network. The local field at a given site depends on the exchange interaction J between these two sublattices, leading to a spin reversal when the magnetic moment of the dysprosium network is larger than the one produced by the ferromagnetic Mn sublattice. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.