Complementary x-ray emission (XES) and x-ray-absorption (XAS) measurements of ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ as a function of temperature have been performed. For $0.5<~x<~0.8$ we find changes in the XAS and XES spectra consistent with a small increase in the average Mn valence accompanying the passage to the low-temperature state. It is suggested that this small Mn-configuration shift could be due to the competition between the energies associated with ferromagnetic (FM) and charge/orbital (CO) correlations. In the region $0.0<~x<~0.4$ we observe thermal spectral changes quite different from those found in the $x>~0.5$ materials. Modest thermal changes in the Mn XAS pre-edge (K-edge), for $0.0<~x<~0.4,$ were observed to be coupled to the robustness of the FM-metallic ground state. The clearest pre-edge feature variation appears to be related to $\mathrm{Mn}{-e}_g$-majority-spin state changes. In contrast the thermal XES spectral changes appear similar in character in the antiferromagnetic (AF)-insulating $x=0.0\mathrm{}$ and FM-metallic $x=0.3\mathrm{}$ materials. An enhancement of the effective local moment via a coupling to the internal exchange field, in the magnetically ordered states, is proposed to explain these XES results. The $x=1.0\mathrm{}$ end member $\left({\mathrm{CaMnO}}_3\right)$ was found to exhibit significant temperature dependence of the absorption and emission spectra. These XAS and XES results, for ${\mathrm{CaMnO}}_3,$ are discussed in terms of thermal perturbations on the degree of covalency of this material.

• Received 3 January 2000

DOI:https://doi.org/10.1103/PhysRevB.62.13472