Ordered states in itinerant magnets may be related to magnetic moments displaying some weak local moment characteristics, as in intermetallic compounds hosting transition metal coordination complexes. In this paper, we report on the Fe K-edge X-ray absorption spectroscopy (XAS) of the itinerant magnets RFe4Sb12 (R =Na, K, Ca, Sr, Ba), aiming at exploring the electronic and structural properties of the octahedral building block formed by Fe and the Sb ligands. We find evidence for strong hybridization between the Fe 3d and Sb 5p states at the Fermi level, giving experimental support to previous electronic structure calculations of the RFe4Sb12 skutterudites. The electronic states derived from Fe 3d Sb 5p mixing are shown to be either more occupied and/or less localized in the cases of the magnetically ordered systems, for which R = Na or K, connecting the local Fe electronic structure to the itinerant magnetic properties. Moreover, the analysis of the extended region of the XAS spectra (EXAFS) suggests that bond disorder may be a more relevant parameter to explain the suppression of the ferromagnetic ordered state in CaFe4Sb12 than the decrease of the density of states.

Magnetic frustration and disorder are key ingredients to prevent the onset of magnetic order. In the disordered hexagonal double perovskite BaTi 1/2 Mn 1/2 O3, Mn 4+ cations, with S = 3/2 spins, can either form highly correlated states of magnetic trimers or dimers or remain as weakly interacting orphan spins. At low temperature (T ), the dimer response is negligible, and magnetism is dominated by the trimers and orphans. To explore the role of magnetic frustration, disorder and possibly of quantum fluctuations, the low-T magnetic properties of the remaining magnetic degrees of freedom of BaTi 1/2 Mn 1/2 O3 are investigated. Heat-capacity data and magnetic susceptibility display no evidence for a phase transition to a magnetically ordered phase but indicate the formation of a correlated spin state. The low-temperature spin dynamics of this state is then explored by µSR experiments. The zero field µ + relaxation rate data show no static magnetism down to T = 19 mK and longitudinal field experiments support as well that dynamic magnetism persists at low T . Our results are interpreted in terms of a spin glass state which stems from a disordered lattice of orphans spins and trimers. A spin liquid state in BaTi 1/2 Mn 1/2 O3, however, is not excluded and is also discussed.

Engineering of thermoelectric materials requires an understanding of thermal conduction by lattice and electronic degrees of freedom. Filled skutterudites denote a large family of materials suitable for thermoelectric applications where reduced lattice thermal conduction attributed to localized lowfrequency vibrations (rattling) of filler cations inside large cages of the structure. In this work, a multiwavelength method of exploiting X-ray dynamical diffraction in single crystals of CeFe 4 P 12 is presented and applied to resolve the atomic amplitudes of vibrations. The results suggest that the vibrational dynamics of the whole filler-cage system is the actual active mechanism behind the optimization of thermoelectric properties.

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