Room-Temperature Type-II Multiferroic Phase Induced by Pressure in Cupric Oxide.

According to previous theoretical work, the binary oxide CuO can become a room-temperature multiferroic via tuning of the superexchange interactions by application of pressure. Thus far, however, there has been no experimental evidence for the predicted room-temperature multiferroicity. Here, we show by neutron diffraction that the multiferroic phase in CuO reaches 295 K with the application of 18.5 GPa pressure. We also develop a spin Hamiltonian based on density functional theory and employing superexchange theory for the magnetic interactions, which can reproduce the experimental results. The present Letter provides a stimulus to develop room-temperature multiferroic materials by alternative methods based on existing low temperature compounds, such as epitaxial strain, for tunable multifunctional devices and memory applications.

Magnetically Induced Polarization in Centrosymmetric Bonds.

We reveal the microscopic origin of electric polarization P[over →] induced by noncollinear magnetic order. We show that in Mott insulators, such P[over →] is given by all possible combinations of position operators r[over →][over ^]_{ij}=(r[over →]_{ij}^{0},r[over →]_{ij}) and transfer integrals t[over ^]_{ij}=(t_{ij}^{0},t_{ij}) in the bonds, where r[over →]_{ij}^{0} and t_{ij}^{0} are spin-independent contributions in the basis of Kramers doublet states, while r[over →]_{ij} and t_{ij} stem solely from the spin-orbit interaction. Among them, the combination t_{ij}^{0}r[over →]_{ij}, which couples to the spin current, remains finite in the centrosymmetric bonds, thus yielding finite P[over →] in the case of noncollinear arrangement of spins. The form of the magnetoelectric coupling, which is controlled by r[over →]_{ij}, appears to be rich and is not limited to the phenomenological law P[over →]∼ε_{ij}×[e_{i}×e_{j}] with ε_{ij} being the bond vector connecting the spins e_{i} and e_{j}. Using density-functional theory, we illustrate how the proposed mechanism works in the spiral magnets CuCl_{2}, CuBr_{2}, CuO, and α-Li_{2}IrO_{3}, providing a consistent explanation for the available experimental data.

RhII -Catalyzed De-symmetrization of Ethane-1,2-dithiol and Propane-1,3-dithiol Yields Metallo-ß-lactamase Inhibitors.

Diversity-oriented synthesis (DOS) is a rich source for novel lead structures in Medicinal Chemistry. In this study, we present a DOS-compatible method for synthesis of compounds bearing a free thiol moiety. The procedure relies on Rh(II)-catalyzed coupling of dithiols to diazo building blocks. The synthetized library was probed against metallo-ß-lactamases (MBLs) NDM-1 and VIM-1. Biochemical and biological evaluation led to identification of novel potent MBL inhibitors with antibiotic adjuvant activity.

Giant contribution of the ligand states to the magnetic properties of the Cr2Ge2Te6 monolayer.

The magnetic properties of the Cr2Ge2Te6 monolayer - an important two-dimensional (2D) ferromagnetic (FM) material - are systematically investigated on the basis of ab initio electronic structure calculations within density functional theory (DFT). For these purposes we construct a minimal tight-binding model in the basis of maximally localized Wannier functions, which describes the behavior of the magnetic Cr 3d, Ge 4p, and Te 5p electrons. This model allows us to rationalize the results of conventional DFT calculations at the microscopic level. We explore the abilities of different techniques, including the Green's function perturbation theory and constraint calculations with an external magnetic field, for the analysis of magnetic interactions, that allow us to decompose these interactions in terms of partial contributions coming from different atomic sites. We argue that, although the magnetism of Cr2Ge2Te6 originates from the Hund's rule effects in the partially filled Cr 3d shell, the contributions of the ligand - and particularly Te 5p - states are crucially important and have a significant effect on the behavior of isotropic exchange interactions, magnetocrystalline anisotropy energy (MAE), and antisymmetric Dzyaloshinskii-Moriya (DM) interactions induced by an electric field. In particular, the Te 5p states increase dramatically the FM coupling and DM interactions between the Cr spins. They are also largely responsible for the behavior of MAE, manifesting themselves in non-Heisenberg type effects, which go beyond the scopes of the conventional Mermin-Wagner theorem for the analysis of 2D magnetism of Cr2Ge2Te6.

Magnetism of NaFePO4 and related polyanionic compounds.

Magnetic properties of maricite (m) and triphlyte (t) polymorphs of NaFePO4 are investigated by combining ab initio density functional theory with a model Hamiltonian approach, where a realistic Hubbard-type model for magnetic Fe 3d states in NaFePO4 is constructed entirely from first-principles calculations. For these purposes, we perform a comparative study based on the pseudopotential and linear muffin-tin orbital methods while tackling the problem of parasitic non-sphericity of the exchange-correlation potential. Upon calculating the model parameters, magnetic properties are studied by applying the mean-field Hartree-Fock approximation and the theory of superexchange interactions to extract the corresponding interatomic exchange parameters. Despite some differences, the two methods provide a consistent description of the magnetic properties of NaFePO4. On the one hand, our calculations reproduce the correct magnetic ordering for t-NaFePO4 allowing for magnetoelectric effect, and the theoretical values of Néel and Curie-Weiss temperatures are in fair agreement with reported experimental data. Furthermore, we investigate the effect of chemical pressure on magnetic properties by substituting Na with Li and, in turn, we explain how a noncollinear magnetic alignment induced by an external magnetic field leads to magnetoelectric effect in NaFePO4 and other transition-metal phosphates. However, the origin of a magnetic superstructure with q = (1/2, 0, 1/2) observed experimentally in m-NaFePO4 remains puzzling. Instead, we predict that competing exchange interactions can lead to the formation of magnetic superstructures along the shortest orthorhombic c axis of m-NaFePO4, similar to multiferroic manganites.

Luminescence Thermochromism of Gold(I) Phosphane-Iodide Complexes: A Rule or an Exception?

A series of gold(I) iodide complexes 1-11 have been prepared from di-, tri-, and tetraphosphane ligands. Crystallographic studies reveal that the di- (1-7) and tetrametallic (11) compounds feature linearly coordinated gold(I) ions with short aurophilic contacts. Their luminescence behavior is determined by the combined influence of the phosphane properties, metal-metal interaction, and intermolecular lattice-defined interactions. The proposed variable contribution of 3 (X+M)-centered (X=halogen; M=metal) and 3 XLCT (halogen to ligand charge transfer) electronic transitions into the lowest lying excited state, which is influenced by supramolecular packing, is presumably responsible for the alteration of room-temperature emission color from green (λ=545 nm, for 11) to near-IR (λ=698 nm, for 2). Dinuclear compounds 6 and 7 exhibit distinct luminescence thermochromism with a blueshift up to 5750 cm-1 upon cooling. Such dramatic change of emission energy is assigned to the presence of two coupled triplet excited states of 3 ππ* and 3 (X+M)C/3 XLCT nature, the presence of which depends on both molecular structure and the crystal lattice arrangement.

Electronic structure of strongly correlated systems emerging from combining path-integral renormalization group with the density-functional approach.

A new scheme of first-principles computation for strongly correlated electron systems is proposed. This scheme starts from the local-density approximation (LDA) at high-energy band structure, while the low-energy effective Hamiltonian is constructed by a downfolding procedure using combinations of the constrained-LDA and the GW method. The obtained low-energy Hamiltonian is solved by the path-integral renormalization-group method, where spatial and dynamical fluctuations are fully considered. An application to Sr2VO4 shows that the scheme is powerful in agreement with experimental results. It further predicts a nontrivial orbital-stripe order.