Anisotropic three-dimensional magnetism in CaFe2As2

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

Spin-wave dispersion in magnetostrictive Fe-Ga alloys: Inelastic neutron scattering measurements

Fe-Ga alloys of appropriate Ga concentration and heat treatment show a very large enhancement in the tetragonal magnetostriction over that of pure alpha-Fe [lambda(100)(Fe-Ga)similar to 15 lambda(100)(Fe)]. In order to gain further understanding of the extraordinary magnetoelastic characteristics of this system, the spin dynamics of two of these alloys, Fe1-xGax (x=0.160 and 0.225), were studied using inelastic neutron scattering techniques. The correlation of the spin-wave dispersion curve with the lattice constant and atomic radii of solute is examined for this and other Fe alloys

Antiferromagnetism in alpha-Li3Fe2(PO4)(3)

Neutron diffraction techniques have been used to determine the magnetic structure of Fe in monoclinic alpha -Li3Fe2(PO4)(3). Rietveld analysis of the room temperature powder diffraction pattern confirms the monoclinic structure of the sample and is in agreement with previous studies. At low temperatures a paramagnetic to antiferromagnetic transition is observed at T-N = 30.0 K. Our analysis shows that at T = 4 K the two inequivalent Fe sites have antiparallel magnetic moments that are aligned along the a-axis. The average magnetic moment, gS = 5.0 mu (B) indicates homogeneous Fe3+ (S = 5/2). (C) 2001 Elsevier Science B.V. All rights reserved.234340140

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

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

Anomalous spin waves and the commensurate-incommensurate magnetic phase transition in LiNiPO4

Detailed spin-wave spectra of magneto-electric LiNiPO4 have been measured by neutron scattering at low temperatures in the commensurate (C) antiferromagnetic (AF) phase with ordering temperature 20.8 K. An anomalous low-energy mode is observed at the modulation vector of the incommensurate (IC) AF phase appearing above the 20.8 K. A linear spin-wave model based on Heisenberg exchange couplings and single ion anisotropies accounts for all the observed spin-wave dispersions and intensities. Along the b axis an unusually strong next-nearest-neighbor AF coupling competes with the dominant nearest-neighbor AF exchange interaction and causes the IC structure.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.

Phase separation and doped-hole segregation in La2CuO4+δ and La2-xSrxCuO4+δ

Herein, we review the magnetic, superconducting and structural phase diagrams of the title systems, with an emphasis on our recent results form magnetic and structural neutron diffraction, magnetic susceptibility and system, and indicate the occurrence of frustrated phase separation on a nanoscopic length scale in the La Sr CuO system with O < x ≲ 0.05. La nuclear quadrupole resonance measurements. The results clarify the miscibility gap in the La CuO . © 1994. 2- x x 4 2 4+δ 13

Phase separation and doped-hole segregation in La2CuO4+δ and La2-xSrxCuO4+δ

Herein, we review the magnetic, superconducting and structural phase diagrams of the title systems, with an emphasis on our recent results form magnetic and structural neutron diffraction, magnetic susceptibility and system, and indicate the occurrence of frustrated phase separation on a nanoscopic length scale in the La2-xSrxCuO4 system with O < x ≲ 0.05. 139La nuclear quadrupole resonance measurements. The results clarify the miscibility gap in the La2CuO4+δ. © 1994

Monte Carlo simulation study of magnetic properties of Fe-doped Li3V2(PO4)3

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