128 research outputs found
Intertwined magnetic and nematic orders in semiconducting KFeAgTe
Superconductivity in the iron pnictides emerges from metallic parent
compounds exhibiting intertwined stripe-type magnetic order and nematic order,
with itinerant electrons suggested to be essential for both. Here we use X-ray
and neutron scattering to show that a similar intertwined state is realized in
semiconducting KFeAgTe (KFeAgTe) without
itinerant electrons. We find Fe atoms in KFeAgTe form
isolated blocks, separated by nonmagnetic Ag atoms. Long-range
magnetic order sets in below K, with magnetic moments
within the Fe blocks ordering into the stripe-type configuration. A
nematic order accompanies the magnetic transition, manifest as a structural
distortion that breaks the fourfold rotational symmetry of the lattice. The
nematic orders in KFeAgTe and iron pnictide parent
compounds are similar in magnitude and how they relate to the magnetic order,
indicating a common origin. Since KFeAgTe is a
semiconductor without itinerant electrons, this indicates that local-moment
magnetic interactions are integral to its magnetic and nematic orders, and such
interactions may play a key role in iron-based superconductivity.Comment: supplemental material available upon request, to be published in PR
Structural, electronic and magnetic properties of SrRuO under epitaxial strain
Using density functional theory within the local spin density approximation,
structural, electronic and magnetic properties of SRO are investigated. We
examine the magnitude of the orthorhombic distortion in the ground state and
also the effects of applying epitaxial constraints, whereby the influence of
large (in the range of ) in-plane strain resulting from coherent
epitaxy, for both [001] and [110] oriented films, have been isolated and
investigated. The overall pattern of the structural relaxations reveal coherent
distortions of the oxygen octahedra network, which determine stability of the
magnetic moment on the Ru ion. The structural and magnetic parameters exhibit
substantial changes allowing us to discuss the role of symmetry and
possibilities of magneto-structural tuning of \SRO-based thin film structures.Comment: 11 page
Growth and Characterization of Ce- Substituted Nd2Fe14B Single Crystals
Single crystals of (Nd1-xCex)2Fe14B are grown out of Fe-(Nd,Ce) flux.
Chemical and structural analysis of the crystals indicates that
(Nd1-xCex)2Fe14B forms a solid solution until at least x = 0.38 with a
Vegard-like variation of the lattice constants with x. Refinements of single
crystal neutron diffraction data indicate that Ce has a slight site preference
(7:3) for the 4g rare earth site over the 4f site. Magnetization measurements
show that for x = 0.38 the saturation magnetization at 400 K, a temperature
important to applications, falls from 29.8 for the parent Nd2Fe14B to 27.6
(mu)B/f.u., the anisotropy field decreases from 5.5 T to 4.7 T, and the Curie
temperature decreases from 586 to 543 K. First principles calculations carried
out within density functional theory are used to explain the decrease in
magnetic properties due to Ce substitution. Though the presence of the
lower-cost and more abundant Ce slightly affects these important magnetic
characteristics, this decrease is not large enough to affect a multitude of
applications. Ce-substituted Nd2Fe14B is therefore a potential high-performance
permanent magnet material with substantially reduced Nd content.Comment: 11 Pages, 8 figures, 5 table
Direct evidence of a zigzag spin chain structure in the honeycomb lattice: A neutron and x-ray diffraction investigation on single crystal
We have combined single crystal neutron and x-ray diffractions to investigate
the magnetic and crystal structures of the honeycomb lattice .
The system orders magnetically below K with Ir ions forming
zigzag spin chains within the layered honeycomb network with ordered moment of
/Ir site. Such a configuration sharply contrasts the
N{\'{e}}el or stripe states proposed in the Kitaev-Heisenberg model. The
structure refinement reveals that the Ir atoms form nearly ideal 2D honeycomb
lattice while the octahedra experience a trigonal distortion that
is critical to the ground state. The results of this study provide much-needed
experimental insights into the magnetic and crystal structure crucial to the
understanding of the exotic magnetic order and possible topological
characteristics in the 5-electron based honeycomb lattice.Comment: Revised version as that to appear in PR
Effect of neutron irradiation on the London penetration depth for polycrystalline Bi(1.8)Pb(0.3)Sr2Ca2Cu3O10 superconductor
Magnetization studies of polycrystalline Bi(1.8)Pb(0.3)Sr2Ca2Cu3O10 superconductor, prior to and after neutron irradiation, showed an increase in J(sub c) due to irradiation damage. Analysis of the equilibrium magnetization revealed significant increases in other more fundamental properties. In particular, the London penetration depth increased by approximately 15 percent following irradiation with 8 x 10(exp 16) neutrons/sq cm. Corresponding changes were observed in the upper critical magnetic field H(sub c2). However, the most fundamental thermodynamic property, the superconductive condensation energy F(sub c), was unaffected by the moderate level of neutron-induced damage
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