Electronic and magnetic phase diagram of polycrystalline Gd1−xCaxMnO3 manganites

Based on the structural and magnetoresistive properties of Gd1−xCaxMnO3 (GCMO) (0≤x≤1) polycrystalline manganites, the magnetic phase diagram of GCMO is deduced. The results show that all of the compounds are ferrimagnetic in the ground state due to polarization of the large magnetic moments of Gd in the opposite direction of Mn ions. However, even disregarding the ordering of the Gd spins in the applied magnetic field direction, the series exhibit complicated magnetic behavior below magnetic ordering temperature (TC or TN). In the hole doped region x≤0.5, Mn ions order ferromagnetically. In the middle doping region (0.5≤x≤0.7), charge ordering can be observed above TN and, below TN, Mn ions are in antiferromagnetic state which is more obvious in the case with x=0.8. In the electron doped region 0.8≤x≤0.9, Mn ions reveal magnetic cluster glass properties. Except for x=0.9, which exhibits degenerate semiconductive behavior, the temperature dependence of resistance shows insulating behavior for all other GCMO concentrations. This can be associated with the small average ionic radius of rare earth cations and colossal magnetoresistance (CMR) is observed for GCMO with x=0.8 and x=0.9 when the applied magnetic field exceeds 9 T.