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Magnetite (Fe$_{3}$O$_{4}$) is a mixed valent system where electronic conductivity occurs on the B-site (octahedral) iron sublattice of the spinel structure. Below $T_{V}=122$ K, a metal-insulator transition occurs which is argued to arise from the charge ordering of 2+ and 3+ iron valences on the B-sites (Verwey transition). Inelastic neutron scattering measurements show that optical spin waves propagating on the B-site sublattice ($sim$80 meV) are shifted upwards in energy above $T_{V}$ due to the occurrence of B-B ferromagnetic double exchange in the mixed valent metallic phase. The double exchange interaction affects only spin waves of $Delta_{5}$ symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by electron correlations above $T_{V}$.
The double exchange model describing interactions of itinerant electrons with localized spins is usually used to explain ferromagnetism in metals. We show that for a variety of crystal lattices of different dimensionalities and for a wide range of mo
We use hard x-ray photoemission spectroscopy (HAXPES) to investigate the electronic structure of YbAl2, for which the Yb valence has not been consistently reported to date. The bulk sensitivity and the analytical simplicity provided by the Yb 3d core
Temperature dependence of magnetization curves of well homogenized samples of Ce(Co$_{1-x}$Cu$_{x}$)$_5$ ($0le x le 0.7$), a family of representative $4f$-$3d$ intermetallic magnets found in rare-earth permanent magnets, is measured. A remarkable enh
Using density functional theory, we study the lattice dynamical properties of magnetite (Fe$_3$O$_4$) in the high-temperature cubic and low-temperature monoclinic phases. The calculated phonon dispersion curves and phonon density of states are compar
We investigated the onset of the many-body coherence in the f-orbital single crystalline alloys Ce(1-x)Yb(x)CoIn5 through thermodynamic and magneto-transport measurements. Our study shows the evolution of the many-body electronic state as the Kondo l