Low temperature behavior of the heavy Fermion Ce3Co4Sn13

The compound Ce3Co4Sn13 is an extremely heavy cubic heavy fermion system with a low temperature electronic specific heat of order ~4 J/mol-K2. If the compound is nonmagnetic, it would be one of the heaviest nonmagnetic Ce-based heavy fermions reported to date and therefore would be expected to lie extremely close to a quantum critical point. However, a broad peak of unknown origin is observed at 0.8 K in the specific heat and magnetic susceptibility, suggesting the possibility of antiferromagnetic order. We present neutron diffraction data from polycrystalline samples which do not show any sign of magnetic scattering below 0.8 K. In addition, we present inelastic neutron scattering data from a single crystal sample which is consistent with the 1.2 K energy scale for Kondo spin fluctuations determined from specific heat measurements.Comment: 4 pages, 2 figures, submitted to J. Mag. Mag. Mater. for ICM 200

Anomalous spin density distribution on oxygen and Ru in Ca1.5_{1.5}Sr0.5_{0.5}RuO4_4: A polarised neutron diffraction study

By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in Ca$_{1.5}$Sr$_{0.5}$RuO$_4$. Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding $\mu$$_{Ru}$ = 0.346(11) $\mu$$_B$, $\mu_{O1}$ = 0.076(6) $\mu$$_B$ and $\mu_{O2}$ = 0.009(6) $\mu$$_B$. The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. %The maximum entropy method is used for the %reconstruction of the magnetization density and reveals a strongly anisotropic The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the {\it xy} ($t_{2g}$ band) {\it d}-orbitals.Comment: 4 pages 3 figure

First-Order Transition to Incommensurate Phase with Broken Lattice Rotation Symmetry in Frustrated Heisenberg Model

We study a finite-temperature phase transition in the two-dimensional classical Heisenberg model on a triangular lattice with a ferromagnetic nearest-neighbor interaction $J_1$ and an antiferromagnetic third-nearest-neighbor interaction $J_3$ using a Monte Carlo method. Apart from a trivial degeneracy corresponding to O(3) spin rotations,the ground state for $J_3 \neq 0$ has a threefold degeneracy corresponding to 120 degree lattice rotations. We find that this model exhibits a first-order phase transition with the breaking of the threefold symmetry when the interaction ratio is $J_3/J_1=-3$.Comment: 4pages,5figure

Raman scattering studies of spin, charge, and lattice dynamics in Ca_{2-x}Sr_{x}RuO_{4} (0 =< x < 0.2)

We use Raman scattering to study spin, charge, and lattice dynamics in various phases of Ca_{2-x}Sr_{x}RuO_{4}. With increasing substitution of Ca by Sr in the range 0 =< x < 0.2, we observe (1) evidence for an increase of the electron-phonon interaction strength, (2) an increased temperature-dependence of the two-magnon energy and linewidth in the antiferromagnetic insulating phase, and (3) evidence for charge gap development, and hysteresis associated with the structural phase change, both of which are indicative of a first-order metal-insulator transition (T_{MI}) and a coexistence of metallic and insulating components for T < T_{MI}

Structural and magnetic aspects of the metal insulator transition in Ca2−x_{2-x}Srx_xRuO4_4

The phase diagram of Ca$_{2-x}$Sr$_x$RuO$_4$ has been studied by neutron diffraction on powder and single-crystalline samples. The experiments reveal antiferromagnetic order and structural distortions characterized by tilts and rotations of the RuO$_6$-octahedra. There is strong evidence that the structural details of the isovalent samples tune the magnetic as well as the electronic behavior. In particular we observe for low Sr-concentration a metal insulator transition associated with a structural change and magnetic ordering

Unusual superexchange pathways in a Ni triangular lattice of NiGa2_2S4_4 with negative charge-transfer energy

We have studied the electronic structure of the Ni triangular lattice in NiGa$_2$S$_4$ using photoemission spectroscopy and subsequent model calculations. The cluster-model analysis of the Ni 2$p$ core-level spectrum shows that the S 3$p$ to Ni 3$d$ charge-transfer energy is $\sim$ -1 eV and the ground state is dominated by the $d^9L$ configuration ($L$ is a S 3$p$ hole). Cell perturbation analysis for the NiS$_2$ triangular lattice indicates that the strong S 3$p$ hole character of the ground state provides the enhanced superexchange interaction between the third nearest neighbor sites.Comment: 10 pages, 5 figures, accepted to PR