Structural and magnetic phase diagram of the two-electron-doped (Ca1-xCex)MnO3 system: Effects of competition among charge, orbital, and spin orderingстатья
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Аннотация:The crystallographic and magnetic phase diagram of the two-electron-doped system (Ca1-x2+Cex4+)MnO3 with 0less than or equal toxless than or equal to0.167 has been determined using neutron powder diffraction, synchrotron x-ray powder diffraction, small angle scattering, and ac susceptibility. In general, the phase diagram is similar to those for other chemically substituted CaMnO3 systems as viewed as a function of the Mn charge state. Thus, when viewed as a function of the Ce concentration x the phase diagram is compressed by a factor of 2. Particular differences, such as a broad compositional region (0.1less than or equal toxless than or equal to0.167) at room temperature in which the crystallographic structure is monoclinic, originate from the small size of the Ce4+ ion. Two-phase behavior is observed over a large compositional region (0.1less than or equal toxless than or equal to0.167) at low temperature. The experimental data argue against chemical inhomogeneity or strain arising from grain/domain interaction stresses as explanations for the phase separation. Thus, the extended region of phase coexistence is postulated to originate from the subtle competition among charge, orbital, and spin ordering that may be initiated by A-site cation disorder effect and is then stabilized by an energy barrier between different magnetic ordering that develops in the two phases.