Gapless Quantum Spin Liquid in the Triangular System Sr_{3}CuSb_{2}O_{9}.

We report gapless quantum spin liquid behavior in the layered triangular Sr_{3}CuSb_{2}O_{9} system. X-ray diffraction shows superlattice reflections associated with atomic site ordering into triangular Cu planes well separated by Sb planes. Muon spin relaxation measurements show that the S=1/2 moments at the magnetically active Cu sites remain dynamic down to 65 mK in spite of a large antiferromagnetic exchange scale evidenced by a large Curie-Weiss temperature θ_{CW}≃-143 K as extracted from the bulk susceptibility. Specific heat measurements also show no sign of long-range order down to 0.35 K. The magnetic specific heat (C_{m}) below 5 K reveals a C_{m}=γT+αT^{2} behavior. The significant T^{2} contribution to the magnetic specific heat invites a phenomenology in terms of the so-called Dirac spinon excitations with a linear dispersion. From the low-T specific heat data, we estimate the dominant exchange scale to be ∼36 K using a Dirac spin liquid ansatz which is not far from the values inferred from microscopic density functional theory calculations (∼45 K) as well as high-temperature susceptibility analysis (∼70 K). The linear specific heat coefficient is about 18 mJ/mol K^{2} which is somewhat larger than for typical Fermi liquids.

On Fe-Fe Dumbbells in the Ideal and Real Structures of FeGa3.

The intermetallic phase FeGa3 belongs to the rare examples of substances with transition metals where semiconducting behavior is found. The necessary electron count of 17 ve/fu can be formally derived from eight Fe-Ga and one Fe-Fe two-center-two-electron bond. The situation is reminiscent of the well-known Fe2(CO)9 scenario, where a direct Fe-Fe two-center-two-electron bond was shown to not be present. Fe-Fe interaction in FeGa3 and its substitution variants represents the crucial point for explanation of electronic, thermal transport, and optical properties of this material. Chemical bonding analysis in position space of FeGa3 and Fe2(CO)9 on the basis of the topology of the electron localizability indicator distribution, QTAIM atoms, two- and three-center delocalization indices, domain natural orbitals, IQA analysis, and an evaluation of the Fe-Fe dissociation energy yields a complete picture of the partially compensated Fe-Fe bond, which is nevertheless strong enough to be of decisive importance. Structural reinvestigation of differently synthesized single crystals leads to the composition Fe1+ xGa3 (0 ≤ x ≤ 0.018), where the additional Fe atoms are predicted from DFT/PBE calculations to yield a magnetic moment of about 2 µB/Fe2 atom and metallic in-gap states. Accompanying magnetization and ESR measurements are consistent with this picture.

Spin Dynamics of (Sc[Formula: see text]Lu[Formula: see text])[Formula: see text]In Studied by Electron Spin Resonance.

The electron spin resonance (ESR) of conduction electrons is reported for the weak itinerant ferromagnet Sc[Formula: see text]In which, upon chemical substitution with Lu, shows a suppression of ferromagnetic correlations. A well-defined ESR lineshape of Dysonian type characterizes the spectra. The ESR linewidth, determined by the spin dynamics, displays a broad minimum only for the Sc[Formula: see text]In compound. We discuss the results using the mechanism of exchange enhancement of spin-lifetimes.

Ca12 [Mn19 N23 ] and Ca133 [Mn216 N260 ]: Structural Complexity by 2D Intergrowth.

Two new calcium nitridomanganates, Ca12 [Mn19 N23 ] (P3, a=11.81341(3) Å, c=5.58975(2) Å, Z=1) and Ca133 [Mn216 N260 ] (P3‾ , a=39.477(1) Å, c=5.5974(2) Å, Z=1), were obtained by a gas-solid reaction of Ca3 N2 and Mn with N2 at 1273 K and 1223 K, respectively. The crystal structure of Ca12 [Mn19 N23 ] was determined from high-resolution X-ray synchrotron powder diffraction data, whereas single-crystal X-ray diffraction was employed to establish the crystal structure of the Ca133 [Mn216 N260 ] phase, which classifies as a complex metallic alloy (CMA). Both crystal structures have 2D nitridomanganate layers containing similar building blocks but of different levels of structural complexity. Bonding analysis as well as magnetic susceptibility and electron spin resonance measurements revealed that only a fraction of the Mn atoms in both structures carries a localized magnetic moment, while for most Mn species the magnetism is quenched as a result of metal-metal bond formation.

Electron spin resonance study on the 4fhoneycomb quantum magnet YbCl3.

The local magnetic properties of Yb3+in the layered honeycomb material YbCl3were investigated by electron spin resonance on single crystals. For in-plane and out-of-plane field orientations theg-factor shows a clear anisotropy (g∥=2.97(8)andg⊥=1.53(4)), whereas the low temperature exchange coupling and the spin relaxation display a rather isotropic character. At elevated temperatures the contribution of the first excited crystal field level (21±2meV) dominates the spin relaxation.

Electron spin resonance of the itinerant ferromagnets LaCrGe3, CeCrGe3and PrCrGe3.

We report electron spin resonance of the itinerant ferromagnets LaCrGe3, CeCrGe3, and PrCrGe3. These compounds show well defined and very similar spectra of itinerant Cr 3dspins in the paramagnetic temperature region. Upon cooling and crossing the Cr-ferromagnetic ordering (below around 90 K) strong spectral structures start to dominate the resonance spectra in a quite different manner in the three compounds. In the Ce- and Pr-compounds the resonance is only visible in the paramagnetic region whereas in the La-compound the resonance can be followed far below the ferromagnetic ordering temperature. This behavior will be discussed in terms of the specific interplay between the 4fand 3dmagnetism which appears quite remarkable since CeCrGe3displays heavy fermion behavior even in the magnetically ordered state.

Magnetic and Electronic Properties of Weyl Semimetal Co2MnGa Thin Films.

Magnetic Weyl semimetals are newly discovered quantum materials with the potential for use in spintronic applications. Of particular interest is the cubic Heusler compound Co2MnGa due to its inherent magnetic and topological properties. This work presents the structural, magnetic and electronic properties of magnetron co-sputtered Co2MnGa thin films, with thicknesses ranging from 10 to 80 nm. Polarized neutron reflectometry confirmed a uniform magnetization through the films. Hard x-ray photoelectron spectroscopy revealed a high degree of spin polarization and localized (itinerant) character of the Mn d (Co d) valence electrons and accompanying magnetic moments. Further, broadband and field orientation-dependent ferromagnetic resonance measurements indicated a relation between the thickness-dependent structural and magnetic properties. The increase of the tensile strain-induced tetragonal distortion in the thinner films was reflected in an increase of the cubic anisotropy term and a decrease of the perpendicular uniaxial term. The lattice distortion led to a reduction of the Gilbert damping parameter and the thickness-dependent film quality affected the inhomogeneous linewidth broadening. These experimental findings will enrich the understanding of the electronic and magnetic properties of magnetic Weyl semimetal thin films.

Electron spin resonance on the spin-1/2 triangular magnet NaYbS2.

The delafossite structure of NaYbS2 contains a planar spin-1/2 triangular lattice of Yb3+ ions and features a possible realisation of a quantum spin-liquid state. We investigated the Yb3+ spin dynamics by electron spin resonance (ESR) in single-crystalline samples of NaYbS2. Very clear spectra with a well-resolved and large anisotropy could be observed down to the lowest accessible temperature of 2.7 K. In contrast to the ESR properties of other known spin-liquid candidate systems, the resonance seen in NaYbS2 is accessible at low fields (<1 T) and is narrow enough for accurate characterisation of the relaxation rate as well as the g factor of the Yb3+ spins.

Microscopic investigation of low dimensional magnet Sc2Cu2O5: combined experimental and ab initio approach.

Sc2Cu2O5 is a non centro-symmetric oxide comprising of zig-zag chains made up of Cu2+ ions in a distorted square planer coordination. We present here a combined experimental and theoretical investigation on this compound, which is based on magnetization, electron spin resonance (ESR), heat capacity as well as density functional theory (DFT) based calculations. Short range magnetic correlation prior to the long range order at [Formula: see text] K is evidenced by a broad hump like feature ([Formula: see text]43 K) found in the magnetic contribution of the heat capacity as well as by deviations from a regular Curie-Weiss behavior observed in the bulk magnetization and the Cu2+ ESR intensity. The DFT results indicate the existence of ferro-orbital ordering at the Cu-sites, which gives rise to chain like arrangements of Cu ions along the crystallographic b axis. It also signifies complex nature of the spin structure with nonuniform magnetic interactions along the zig-zag chains. The ground state energy is found to be minimum for ferromagnetically coupled spin-dimers along the chains, whereas the adjacent chains are themselves antiferromagnetically coupled. The experimentally observed short range magnetic correlations possibly arise due to this chain like structure.

Spin dynamics of FeGa3-x Ge x studied by electron spin resonance.

The intermetallic semiconductor FeGa3 acquires itinerant ferromagnetism upon electron doping by a partial replacement of Ga with Ge. We studied the electron spin resonance (ESR) of high-quality single crystals of FeGa3-x Ge x for x from 0 up to 0.162 where ferromagnetic order is observed. For x = 0 we observed a well-defined ESR signal, indicating the presence of pre-formed magnetic moments in the semiconducting phase. Upon Ge doping the occurrence of itinerant magnetism clearly affects the ESR properties below ≈40 K, whereas at higher temperatures an ESR signal as seen in FeGa3 prevails independent on the Ge content. The present results show that the ESR of FeGa3-x Ge x is an appropriate and direct tool to investigate the evolution of 3d-based itinerant magnetism.