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Budko, S L

Publications and source records attributed to Budko, S L.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Inelastic Neutron Scattering Study of a Nonmagnetic Collapsed Tetragonal Phase in Nonsuperconducting CaFe2As2: Evidence of the Impact of Spin Fluctuations on Superconductivity in the Iron-Arsenide Compounds

The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Magnetic excitations in underdoped Ba(Fe1-xCox)2As2 with x=0.047

The magnetic excitations in the paramagnetic-tetragonal phase of underdoped Ba(Fe0.953Co0.047)2As2, as measured by inelastic neutron scattering, can be well described by a phenomenological model with purely diffusive spin dynamics. At low energies, the spectrum around the magnetic ordering vector QAFM consists of a single peak with elliptical shape in momentum space. At high energies, this inelastic peak is split into two peaks across the direction perpendicular to QAFM. We use our fittings to argue that such a splitting is not due to incommensurability or propagating spin-wave excitations, but is rather a consequence of the anisotropies in the Landau damping and in the magnetic correlation length, both of which are allowed by the tetragonal symmetry of the system. We also measure the magnetic spectrum deep inside the magnetically ordered phase, and find that it is remarkably similar to the spectrum of the paramagnetic phase, revealing the strongly overdamped character of the magnetic excitations.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Magnetic and structural transitions in the iron-chalcogenide high-Tc superconductor: K0.8Fe1.76Se2.00

Fe-57 Mossbauer spectroscopy was used to study single-crystals of K0.8Fe1.76Se2.00 from 6K to 673 K. At 6K, the hyperfine field (B-hf) is canted away from the c-axis by 18 +/- 3 degrees. The temperature dependence of B-hf follows a spin wave model with a spin excitation gap of 9 +/- 1 meV. A sudden increase in the linewidth and a corresponding drop in (1/2)eQV(zz) at T-N - 532K are indications of strong coupling between the magnetic and structural transitions. (C) 2012 American Institute of Physics.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Competition between stripe and checkerboard magnetic instabilities in Mn-doped BaFe2As2

The appearance of unconventional superconductivity often requires the suppression of an antiferromagnetic (AFM) ordered state by tuning the chemical composition. In BaFe2As2, the AFM ordered state is driven by Fermi surface nesting, resulting in stripe magnetic ordering with propagation vector Qstripe = (; 0) (in Fe square lattice notation). Co substitution acts as an electron donor that destabilizes the nesting condition,1 leading to suppression of the stripe AFM ordering2 and the appearance of superconductivity.3,4 Mn is nominally the hole-doping counterpart of Co which should also detune the Fermi surface nesting, but it is not a superconductor.5 Here we report that Mn doping does not act solely as a hole donor, but instead introduces strong spin uctuations at a wavevector (; ) that is unrelated to the Fermi surface topology of BaFe2As2. Spin uctuations at (; ) and (; 0) coexist, suggesting the Mn dopants act as local magnetic impurities that polarize neighbouring Fe/Mn spins, potentially disrupting superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Magnetic structure of Gd[subscript 5]Ge[subscript 4]

Gd{sub 5}Ge{sub 4} crystallizes in the orthorhombic space group Pnma, and orders antiferromagnetically below the Neel temperature T{sub N} {approx} 127 K. We have employed x-ray resonant magnetic scattering to elucidate the details of the magnetic structure. The magnetic unit cell is the same as the chemical unit cell. From azimuth scans and the Q dependence of the magnetic scattering, all three Gd sites in the structure were determined to be in the same magnetic space group Pnma. The magnetic moments are primarily aligned along the c axis and the c components of the magnetic moments at the three different sites are equal. The ferromagnetic Gd-rich slabs are stacked antiferromagnetically along the b direction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗