Temperature-dependent EXAFS study of local structural distortions in multivalent pristine and modified La0.5Ba0.5CoO2.85 by pulsed 140 T fie

The main goal of this proposal is a high-resolution temperature-dependent EXAFS study at the Co K-edge on the well-characterized pristine and modified La0.5Ba0.5CoO2.85 by pulsed semi-destructive 140 T magnetic field (LNCMI-CNRS, Toulouse) in order to elucidate the most reliable model explaining small local and long-range lattice distortions in the range of the unusual spin-state transitions.
A combination of EXAFS results with our synchrotron/neutron diffraction data (Fig.1b+c) and theoretical calculations will allow us to gain new fundamental insights into the nature of AFM to FM transition (Fig.1c) by clarifying spin-states in each phase, i.e. compare of the models Co3+(HS)+Co4+(IS) into Co3+(HS→IS→LS)+growth of cooperative Jahn-Teller Co4+(LS) [5] or dynamic(only EXAFS identifies) Jahn-Teller Co2+(LS) [9,10] with FM/AFM phase changes (chemical/applied pressure) and anomalous growth of Co and O isotropic ADP (Fig.1b+inset).