Excitations in the field-induced quantum spin liquid state of α-RuCl3

The celebrated Kitaev quantum spin liquid (QSL) is the paradigmatic example of a topological magnet with emergent excitations in the form of Majorana Fermions and gauge fluxes. Upon breaking of time-reversal symmetry, for example in an external magnetic field, these fractionalized quasiparticles acquire non-Abelian exchange statistics, an important ingredient for topologically protected quantum computing. Consequently, there has been enormous interest in exploring possible material realizations of Kitaev physics and several candidate materials have been put forward, recently including α-RuCl3. In the absence of a magnetic field this material orders at a finite temperature and exhibits low-energy spin wave excitations. However, at moderate energies, the spectrum is unconventional and the response shows evidence for fractional excitations. Here we use time-of-flight inelastic neutron scattering to show that the application of a sufficiently large magnetic field in the honeycomb plane suppresses the magnetic order and the spin waves, leaving a gapped continuum spectrum of magnetic excitations. Our comparisons of the scattering to the available calculations for a Kitaev QSL show that they are consistent with the magnetic field induced QSL phase.The work at ORNL’s Spallation Neutron Source and the High Flux Isotope Reactor was supported by the United States Department of Energy (US-DOE), Office of Science - Basic Energy Sciences (BES), Scientific User Facilities Division. Part of the research was supported by the US-DOE, Office of Science - BES, Materials Sciences and Engineering Division (P.K., C.A.B. and J-Q.Y.). D.M. and P.K. acknowledge support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4416. The work at Dresden was in part supported by DFG grant SFB 1143 (J.K. and R.M.). J.K. is supported by the Marie Curie Programme under EC Grant agreements No.703697

Magnetic Frustration Driven by Itinerancy in Spinel CoV2O4

Localized spins and itinerant electrons rarely coexist in geometrically-frustrated spinel lattices. They exhibit a complex interplay between localized spins and itinerant electrons. In this paper, we study the origin of the unusual spin structure of the spinel CoV2O4, which stands at the crossover from insulating to itinerant behavior using the first principle calculation and neutron diffraction measurement. In contrast to the expected paramagnetism, localized spins supported by enhanced exchange couplings are frustrated by the effects of delocalized electrons. This frustration produces a non-collinear spin state even without orbital orderings and may be responsible for macroscopic spin-glass behavior. Competing phases can be uncovered by external perturbations such as pressure or magnetic field, which enhances the frustration

Structural characterization and thermal conductivity of type-I tin clathrates

Three tin compounds, Cs8Sn44, Cs8Ga8Sn38, and Cs8Zn4Sn42, representative of the type-I clathrate hydrate crystal structure are structurally characterized by temperature-dependent neutron powder diffraction, 87 K Sn-119 Mossbauer spectroscopy, and room-temperature single-crystal X-ray diffraction. These compounds form in cubic space group Pm (3) over bar n with alkalimetal atoms residing in the polyhedral cavities formed by the tetrahedrally bonded network of Sn atoms. Of particular interest are the atomic displacement parameters (ADPs) exhibited by the alkali-metal atom inside the polyhedral "cages" formed by the framework Sn atoms. The "guest" Cs atoms inside the larger tetrakaidecahedra show a relatively large room-temperature ADP for Cs8Ga8Sn38 and Cs8Zn4Sn42; however, in the defect Cs8Sn44 compound this is not the case. This is due to two Sn vacancies in Cs8Sn44 which affect the local symmetry and Sn-Sn bonding. Temperature-dependent ADPs for the defect Cs8Sn44 compound are compared to those for Cs8Zn8Sn42. These data help elucidate the cause of the different lattice thermal conductivities of these two compounds

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

Structural, magnetic, and transport properties of La2Cu1-xLixO4.

Li substitutes for Cu in (Formula presented)(Formula presented) up to the limiting stoichiometry (Formula presented)(Formula presented)(Formula presented)(Formula presented), which has superstructure order. The effects of this in-plane hole doping on the structural and magnetic properties of (Formula presented)(Formula presented) are very similar to those due to Sr substitution. The tetragonal-orthorhombic structural phase transition occurs, for a given amount of Sr or Li, at nearly the same temperature, and the in-plane lattice constant of (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) at room temperature depends only on the combined hole count (x+y) and not on the individual Sr or Li concentration. Long-range magnetic order is destroyed upon substituting 3% Li for Cu, analogous to the effect of Sr substitution on (Formula presented). However, the holes introduced by Li substitution are bound. The resistivity as a function of temperature is nonmetallic for all Li concentrations. © 1996 The American Physical Society

Structural, magnetic, and transport properties of La2Cu1-xLixO4.

Li substitutes for Cu in (Formula presented)(Formula presented) up to the limiting stoichiometry (Formula presented)(Formula presented)(Formula presented)(Formula presented), which has superstructure order. The effects of this in-plane hole doping on the structural and magnetic properties of (Formula presented)(Formula presented) are very similar to those due to Sr substitution. The tetragonal-orthorhombic structural phase transition occurs, for a given amount of Sr or Li, at nearly the same temperature, and the in-plane lattice constant of (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) at room temperature depends only on the combined hole count (x+y) and not on the individual Sr or Li concentration. Long-range magnetic order is destroyed upon substituting 3% Li for Cu, analogous to the effect of Sr substitution on (Formula presented). However, the holes introduced by Li substitution are bound. The resistivity as a function of temperature is nonmetallic for all Li concentrations. © 1996 The American Physical Society

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

2Flux growth and characterization of Ce-substituted Nd2Fe14B single crystals

Single crystals of (Nd1−xCex)2Fe14B, some reaching ∼6×8×8mm3 in volume, are grown out of Fe-(Nd, Ce) flux. This crystal growth method allows for large (Nd1−xCex)2Fe14B single crystals to be synthesized using a simple flux growth procedure. Chemical and structural analyses of the crystals indicate 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 at 300 K show only small decreases with increasing Ce content in saturation magnetization (Ms) and anisotropy field (HA), and Curie temperature (TC). First principles calculations are carried out to understand the effect of Ce substitution on the electronic and magnetic properties. For a multitude of applications, it is expected that the advantage of incorporating lower-cost and more abundant Ce will outweigh the small adverse effects on magnetic properties. Ce-substituted Nd2Fe14B is therefore a potential high-performance permanent magnet material with substantially reduced Nd content

Intertwined Magnetic and Nematic Orders in Semiconducting KFe_{0.8}Ag_{1.2}Te_{2}.

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 KFe_{0.8}Ag_{1.2}Te_{2} (K_{5}Fe_{4}Ag_{6}Te_{10}) without itinerant electrons. We find that Fe atoms in KFe_{0.8}Ag_{1.2}Te_{2} form isolated 2×2 blocks, separated by nonmagnetic Ag atoms. Long-range magnetic order sets in below T_{N}≈35  K, with magnetic moments within the 2×2 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 KFe_{0.8}Ag_{1.2}Te_{2} and iron pnictide parent compounds are similar in magnitude and in how they relate to the magnetic order, indicating a common origin. Since KFe_{0.8}Ag_{1.2}Te_{2} 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