Magnetic phase diagrams of the Ln(Mn1-xCox)O-3 (Ln=Eu, Nd, Y) systems

We report magnetization measurements in the Ln(Mn1-xCox)O3+lambda (Ln=Eu, N d; 0 less than or equal to x < 1) and Y(Mn1-xCox)O-3 (0.35 less than or equ al to x less than or equal to 0.5) perovskites as a function of temperature and magnetic field. Compositions in the range of 0.35 less than or equal t o x less than or equal to 0.8 (Ln=Eu), 0.4 less than or equal to x less tha n or equal to 0.6 (Ln=Nd), and 0.35 less than or equal to x less than or eq ual to 0.45 (Ln=Y) exhibit metamagnetic behavior associated with a transfor mation of the magnetic structure from ferrimagnetic, where the magnetic mom ents of Co2+ and Mn4+ ions are antiparallel, to ferromagnetic where they ar e parallel. A ferromagnetic state is observed for the 0.1 less than or equa l to x less than or equal to 0.15 (Ln=Nd) and 0.45 < x less than or equal t o 0.5 (Ln=Y) compositions. Doping and H-T phase diagrams are presented, and these diagrams resemble those of Ln(1-x)Ca(x)MnO(3) charge-ordered mangani tes. Neutron diffraction studies indicate site ordering of the Co and Mn io ns in the Y(Co0.5Mn0.5)O-3 system, which is presumably responsible for its ferromagnetic behavior. (C) 2000 American Institute of Physics. [S0021-8979 (00)01510-3].