MAGNETIC-ORDERING IN PEROVSKITES CONTAINING MANGANESE AND COBALT

The magnetization measurement of systems with the nominal formula R(Mn 1-xCox)O-3 (R = Eu, Gd, Tb, Y) has been made. It has been found that E uMnO3 and GdMnO3 are wet ferromagnets of Dzialoshinsky-Moriya type whe reas TbMnO3 is an antiferromagnet. The substitution of manganese ions by cobalt ones leads to the appearance of different magnetic states: c luster-spin-glass-like (0.1 less than or equal to x less than or equal to 0.3), inhomogeneous ferromagnets with well defined Curie temperatu res (0.4 less than or equal to x less than or equal to 0.8) and again a spin glass state (x greater than or equal to 0.9). Spontaneous magne tizations and Curie temperatures reach maxima for compounds with x = 0 .5. External magnetic field induces a metamagnetic transition in R(Mn0 .5Co0.5)O-3 (R = Gd, Tb, Y). The transition becomes irreversible at lo w temperature in the Tb-and Y-based compounds. The annealing in vacuum of R(Mn0.5Co0.5)O-3 leads to the increase of the Curie temperature an d to the appearance of a metamagnetic transition for the Eu(Mn0.5Co0.5 )O-3 compound. The metamagnetic behaviour is interpreted taking into a ccount the ionic ordering of Co2+ and Mn4+ ions and possible 3d-orbita l ordering in the Co2+ sublattice.