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Coherent x-ray diffraction imaging is used to map the local three dimensional strain inhomogeneity and electron density distribution of two individual LiNi0.5Mn1.5O4-δ cathode nanoparticles in both ex-situ and in-situ environments. Our reconstructed images revealed a maximum strain of 0.4%. We observed different variations in strain inhomogeneity due to multiple competing effects. The compressive/tensile component of the strain is connected to the local lithium content and, on the surface, interpreted in terms of a local Jahn-Teller distortion of Mn3+. Finally, the measured strain distributions are discussed in terms of their impact on competing theoretical models of the lithiation process. [ABSTRACT FROM AUTHOR]

We report on the measurements of current-driven dynamics in magnetic nanopillars as a function of the current-sweep rate. These measurements were intended to verify the recently predicted thermal-activation nature of current-induced precessional states in spin-valve multilayers. For a fixed temperature and field (applied perpendicular to the layers), the critical current for dynamic excitations was found to increase logarithmically with the sweep rate as expected for a thermally activated process. However, we observed little if any dependence of this behavior on temperature. We discuss the implications of this in terms of a simple model of spin-torque driven magnetization dynamics. [ABSTRACT FROM AUTHOR]