Browsing by Author "Montfrooij, W"

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    Ground state of a quantum critical system: neutron scattering on Ce(Ru1-xFex)2Ge2
    (American Physical Society, 2007-08) Montfrooij, W; Lamsal, J; Aronson, M; Bennett, M; De Visser, A; Kai, HY; Huy, NT; Yethiraj, M; Lumsden, MD; Qui, YM
    We present neutron scattering data on Ce(Ru1−xFex)2Ge2 that show that magnetic ordering in the vicinity of a quantum critical point is restricted to short length scales even though all moments that are present have lined up with their neighbors. We argue that order is not limited by crystallographic defects but rather that quantum fluctuations disorder the system and dilute the magnetic moments to such an extent that a percolation network forms. The latter naturally explains how E/T scaling is possible in a system whose apparent dimensionality is above the upper critical dimension. © 2007, American Physical Society
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    Zener double exchange from local valence fluctuations in magnetite
    (American Physical Society, 2007-12-14) McQueeney, RJ; Yethiraj, M; Chang, S; Montfrooij, W; Perring, TG; Honig, JM; Metcalf, P
    Magnetite (Fe3O4) is a mixed valent system where electronic conductivity occurs on the B site (octahedral) iron sublattice of the spinel structure. Below Tv=123 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 (similar to 80 meV) are shifted upwards in energy above Tv due to the occurrence of B-B ferromagnetic double exchange in the mixed valent phase. The double exchange interaction affects only spin waves of Δ5 symmetry, not all modes, indicating that valence fluctuations are slow and the double exchange is constrained by short-range electron correlations above Tv. © 2007, American Physical Society