Browsing by Author "Lumsden, MD"

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    Anisotropic three-dimensional magnetism in CaFe2As2
    (American Physical Society, 2008-11-28) McQueeney, RJ; Diallo, SO; Antropov, VP; Samolyuk, GD; Broholm, C; Ni, N; Nandi, S; Yethiraj, M; Zarestky, JL; Pulikkotil, JJ; Kreyssig, A; Lumsden, MD; Harmon, BN; Canfield, PC; Goldman, AI
    Inelastic neutron scattering measurements of the magnetic excitations in CaFe2As2 indicate that the spin wave velocity in the Fe layers is exceptionally large and similar in magnitude to the cuprates. However, the spin wave velocity perpendicular to the layers is at least half as large that in the layer, so that the magnetism is more appropriately categorized as anisotropic three-dimensional, in contrast to the two-dimensional cuprates. Exchange constants derived from band structure calculations predict spin wave velocities that are consistent with the experimental data. © 2008, American Physical Society
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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