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Information on the phonon density of states of the nanocage-based superconducting clathrates Ba8Si46 and Ba 24Si100 is reported from inelastic neutron scattering experiments. We have observed respectively two Einstein modes corresponding to the two kinds of cages in Ba8Si46 and at least four peaks presumably due to Einstein modes for Ba24Si100. The mode frequencies correspond with results from ab initio lattice dynamics calculations by Tse et al. © 2007 IOP Publishing Ltd.

We report on susceptibility and electron spin resonance (ESR) measurements at X- and Q-band frequencies of Sr2VO4 with orthorhombic symmetry. In this dimer system, the V4+ ions are in tetrahedral environment and are coupled by an antiferromagnetic intradimer exchange constant J/kB≈ 100 K to form a singlet ground state without any phase transitions between room temperature and 2 K. Based on an extended Hückel tight-binding analysis, we identify the strongest exchange interaction to occur between two inequivalent vanadium sites via two intermediate oxygen ions. The ESR absorption spectra can be well fitted by a single Lorentzian line and the temperature dependence of the ESR intensity, and the dc susceptibility can be modeled by using the Bleaney-Bowers approach for independent dimers. The temperature dependence of the ESR linewidth at X-band frequency can be modeled by a superposition of a linear increase with temperature with a slope α =1.35 Oe/K and a thermally activated behavior with an activation energy Δ/kB =1418 K, both of which point to spin-phonon coupling as the dominant relaxation mechanism in this compound. © 2012 American Physical Society.

We report on susceptibility and electron spin resonance (ESR) measurements at X- and Q-band frequencies of Sr2VO4 with orthorhombic symmetry. In this dimer system, the V4+ ions are in tetrahedral environment and are coupled by an antiferromagnetic intradimer exchange constant J/kB≈ 100 K to form a singlet ground state without any phase transitions between room temperature and 2 K. Based on an extended Hückel tight-binding analysis, we identify the strongest exchange interaction to occur between two inequivalent vanadium sites via two intermediate oxygen ions. The ESR absorption spectra can be well fitted by a single Lorentzian line and the temperature dependence of the ESR intensity, and the dc susceptibility can be modeled by using the Bleaney-Bowers approach for independent dimers. The temperature dependence of the ESR linewidth at X-band frequency can be modeled by a superposition of a linear increase with temperature with a slope α =1.35 Oe/K and a thermally activated behavior with an activation energy Δ/kB =1418 K, both of which point to spin-phonon coupling as the dominant relaxation mechanism in this compound. © 2012 American Physical Society.

We report on the optical excitation spectra in Sr2VO 4. The phonon modes are assigned and their evolution with temperature is discussed in the frame of the different phase transitions crossed upon cooling. Besides the expected infrared-active phonons, we observe two additional excitations at about 290 and 840 cm-1, which could correspond to electronic transitions of the V4+ ions. Our experimental results are discussed in the context of recent experimental and theoretical studies of this material with a unique spin-orbital ground state. © 2011 American Physical Society.

We report on the optical excitation spectra in Sr2VO 4. The phonon modes are assigned and their evolution with temperature is discussed in the frame of the different phase transitions crossed upon cooling. Besides the expected infrared-active phonons, we observe two additional excitations at about 290 and 840 cm-1, which could correspond to electronic transitions of the V4+ ions. Our experimental results are discussed in the context of recent experimental and theoretical studies of this material with a unique spin-orbital ground state. © 2011 American Physical Society.