Browsing by Author "Zarestky, JL"

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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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    Neutron scattering study of underdoped Ba(1-x)KxFe2As2 (x=0.09 and 0.17) self-flux-grown single crystals and the universality of the tricritical point
    (American Physical Society, 2012-04-04) Rotundu, CR; Tian, W; Rule, KC; Forrest, TR; Zhao, J; Zarestky, JL; Birgeneau, RJ
    We present a combination of elastic neutron scattering measurements in zero and 14.5 T and magnetization measurements in zero and 14 T on underdoped superconducting Ba(1-x)KxFe2As2 (x=0.09 and 0.17), and the same measurements in zero field on a nonsuperconducting crystal with x = 0.09. The data suggest that the underdoped materials may not be electronic phase separated but rather have slightly inhomogeneous potassium doping. The temperature dependence of the magnetic order parameter below the transition of the sample with x = 0.09 is more gradual than that for the case of the undoped BaFe2As2, suggesting that this doping may be in the vicinity of a tricritical point. We advance therefore the hypothesis that the tricritical point is a common feature of all superconducting 122s. For the x = 0.17 sample, while T-c is suppressed from approximate to 17 to approximate to 8 K by a magnetic field of 14 T, the intensity of the magnetic Bragg peaks (1 0 3) at 1.2 K is enhanced by 10%, showing competition of superconductivity and antiferromagnetism. The intensity of the magnetic Bragg peaks (1 0 3) in the (T-c, T-N) temperature interval remain practically unchanged in 14.5 T within a 10% statistical error. The present results are discussed in the context of the existing literature. © 2012, American Physical Society.