The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

Theory and Software Group - Highlights 2009


Pressure-induced magnetic transition in manganite (La0.75 Ca0.25MnO3)
Y. Ding, D. Haskel, Y.-C. Tseng, E. Kaneshita, M. van Veenendaal, J. F. Mitchell, S. V. Sinogeigin, V. Prakapenka, and H. Mao
Phys. Rev. Lett. 102, 237201 (2009).


Low temperature Mn K-edge x-ray magnetic circular dichroism and x-ray diffraction measurements were carried out to investigate the stability of the ferromagnetic ground state in manganite La0:75Ca0:25MnO3 under nearly uniform compression using diamond anvil cells. The magnetic dichroism signal gradually decreases with pressure and disappears at 23 GPa, and meanwhile a uniaxial compression of MnO6 octahedra along the b axis is observed to continuously increase with pressure and become anomalously large at 23.5 GPa. These changes are attributed to a ferromagnetic-antiferromagnetic transition that is associated with orbital ordering at high pressure.

Dynamics and Spectral Weights of Shake-up Valence Excitations in Resonant Inelastic X-ray Scattering
K. H. Ahn, A. J. Fedro, and Michel van Veenendaal
Phys. Rev. B. 79, 045103 (2009). We discuss the trends in the creation of valence excitations resulting from the screening of the core hole in resonant inelastic x-ray scattering (RIXS) for metals, semiconductors, and strongly correlated systems. We find that the inelastic spectral weight is not determined by the total energy of the shake-up structure, as is expected from simple considerations, but by the excitonic nature of the core hole and the valence electrons. The asymmetry between electron and hole excitations is emphasized and shown to be important in explaining the RIXS spectrum at, e.g., transition-metal K edges.