Diamagnetic Insulator Research Articles

A Novel Diamagnetic Insulating Quadruple Perovskite Oxide YCu<sub>3</sub>Rh<sub>4</sub>O<sub>12</sub>

A novel oxide YCu3Rh4O12 has been obtained using high-pressure and high-temperature conditions of 12 GPa and 1573 K. Electron diffraction and synchrotron X-ray powder diffraction data demonstrates that YCu3Rh4O12 crystallizes in a cubic AA′3B4O12-type quadruple perovskite structure. The valence state is estimated to be Y3+Cu3+3Rh3+4O12 by X-ray absorption spectroscopy. The electric resistivity and magnetization data prove that YCu3Rh4O12 is a diamagnetic insulator, which is expected from the electron configurations of Cu3+ (3d8, low spin, S = 0) and Rh3+ (4d6, low spin, S = 0) ions. The first-principle calculation displays the insulating band structure for YCu3Rh4O12. The valence state transition from Ca2+Cu2.8+3Rh3.4+4O12 to Y3+Cu3+3Rh3+4O12 indicates that the doped electrons by the substitution of Y3+ for Ca2+ are not simply injected to Cu and/or Rh ions, realizing unusual charge redistributions consisting of the simultaneous Cu oxidation (Cu2.8+ → Cu3+) and Rh reduction (Rh3.4+ → Rh3+).

On the formation of spherical aromatic endohedral buckminsterfullerene. Evaluation of M@C60 (M = Cr, Mo, W) from relativistic DFT calculations.

Endohedral metallofullerenes are key species for expanding the range of viable fullerenes, their versatility, and applications. Here we report our computational evaluation on the formation of spherical aromatic counterparts of the C60 fullerene from relativistic DFT calculations, based on the inclusion of Cr, Mo and W endohedral atoms. The resulting M@C60 endohedral fullerenes are 66-π electron neutral species exhibiting bonding properties and electronic structure mimicking the aromaticity and diamagnetic insulator behavior of alkali-C606- phases. The resulting structures are interesting candidates for further experimental realization as novel neutral building blocks for more flexible nanostructured organic materials, highlighting truly spherical aromatic neutral species retaining the truncated icosahedral structure of the seminal Buckminster fullerene.

Transitions from a Kondo-like diamagnetic insulator into a modulated ferromagnetic metal in FeGa3−yGey

One initial and essential question of magnetism is whether the magnetic properties of a material are governed by localized moments or itinerant electrons. Here, we expose the case for the weakly ferromagnetic system FeGa3-y Ge y , wherein these two opposite models are reconciled, such that the magnetic susceptibility is quantitatively explained by taking into account the effects of spin-spin correlation. With the electron doping introduced by Ge substitution, the diamagnetic insulating parent compound FeGa3 becomes a paramagnetic metal as early as at y=0.01, and turns into a weakly ferromagnetic metal around the quantum critical point y=0.15. Within the ferromagnetic regime of FeGa3-y Ge y , the magnetic properties are of a weakly itinerant ferromagnetic nature, located in the intermediate regime between the localized and the itinerant dominance. Our analysis implies a potential universality for all itinerant-electron ferromagnets.

Cu- and Fe-hexacyanoferrate as cathode materials for Potassium ion battery: A First-principles study

In this paper, the efficiency of Iron-Hexacyanoferrate (FeHCF) and Copper-Hexacyanoferrate (CuHCF) as the cathode materials for using in the energy storage application have been investigated using Density Functional Theory. The changes of their lattice parameters due to the insertion of K+ cation were explored. It was found that these changes for CuHCF are less than FeHCF. FeHCF, KFHCF, CuHCF, KCuHCF, and K2CuHCF are found to have a half-metallic nature. In contrast, K2FeHCF is found to be a diamagnetic insulator. K+ diffusion through the FeHCF and CuHCF frameworks have the energy barrier of 1.46eV and 1.00eV, respectively.

Gd-doping-induced insulator-metal transition in SrTiO3

Recently, insulator-metal transition was found experimentally in Gd-doped SrTiO3 films. Here, we present first-principle investigation on the structural, electronic and magnetic properties of Sr1−xGdxTiO3 within density-function theory. The spin-polarized calculations give a diamagnetic insulator at x=0, a ferrimagnetic metal 0.125≤ x≤0.5 and a ferrimagnetic insulator x=1 and all Ti ions moments are antiparallel to Gd ions moments. Magnetic Gd-doping distorts the structures of Sr1−xGdxTiO3 films and results in ferrimagnetism. Doped electrons occupy the bottom of conduction bands so that insulator-metal transition occurs. These calculated results are in agreement with available experiments.

Magnetic effects in sulfur-decorated graphene.

The interaction between two different materials can present novel phenomena that are quite different from the physical properties observed when each material stands alone. Strong electronic correlations, such as magnetism and superconductivity, can be produced as the result of enhanced Coulomb interactions between electrons. Two-dimensional materials are powerful candidates to search for the novel phenomena because of the easiness of arranging them and modifying their properties accordingly. In this work, we report magnetic effects in graphene, a prototypical non-magnetic two-dimensional semi-metal, in the proximity with sulfur, a diamagnetic insulator. In contrast to the well-defined metallic behaviour of clean graphene, an energy gap develops at the Fermi energy for the graphene/sulfur compound with decreasing temperature. This is accompanied by a steep increase of the resistance, a sign change of the slope in the magneto-resistance between high and low fields, and magnetic hysteresis. A possible origin of the observed electronic and magnetic responses is discussed in terms of the onset of low-temperature magnetic ordering. These results provide intriguing insights on the search for novel quantum phases in graphene-based compounds.

Metal–insulator transitions in epitaxial Gd1−Sr TiO3 thin films grown using hybrid molecular beam epitaxy

Abstract Growth of epitaxial Gd 1 − x Sr x TiO 3 thin films using hybrid molecular beam epitaxy and stability of thin films in oxygen rich atmospheres at elevated temperatures are investigated. Only Sr-rich films with x > 0.95 were stable at such conditions. GdTiO 3 is a ferrimagnetic Mott insulator while SrTiO 3 is a diamagnetic band insulator. The metal–insulator transition occurs by electron doping of SrTiO 3 (Gd-doped SrTiO 3 ) or hole doping of GdTiO 3 (Sr-doped GdTiO 3 ). The latter is investigated in more detail. It is shown that the insulating state, even in undoped GdTiO 3 , is dominated by small polaron hopping, which transitions to metallic, Fermi-liquid-type conduction with large amounts of Sr alloying. The metal–insulator transition is also accompanied by transition from n -type to p -type conduction. Furthermore, ferrimagnetism persists into the metallic phase. The results show that the insulating phase is stabilized even for large amounts of Sr doping by polaron formation, and that the transition to the metallic phase occurs via a continuous first order transition and a two phase region.

Electron exchanges in nuclear spin conversion of hydrogen physisorbed on diamagnetic insulators

Models are provided and discussed to interpret new experiments on the ortho-para conversion of hydrogen “physisorbed” on dielectric and diamagnetic surfaces. Electro-static and dynamical molecule-surface interactions complemented by hyperfine contacts are shown to be generally more effective than the magnetic ones. Coulomb repulsion induces exchanges of molecular and surface electrons and excites triplet spin states which are effective in the angular momenta transfers to the catalyst. The conversion time is obtained as the square of a ratio of two energies: the exchange and excitation ones. The main channel is found composed of triplet excitations of the order of the eV, induced by molecule-surface exchanges of about a hundred of meV. It explains the zinc and oxygen rates of about one minute observed on the MOF samples as well as the about ten times slower ones on the ASW. The same mechanism is also shown to occur in the transient regime, but faster. Finally it explains also the conversion of a few hours observed for interstitial hydrogen in silicium by transitions to the conduction band induced by about 10 meV electron exchanges. The molecule-surface orbital geometries of the MOF and ASW configurations are displayed and the quantum path when unfolded exhibits the successive broken symmetries.

Giant Photoconductivity in NMQ[Ni(dmit)2

AbstractThe simple molecular salt NMQ[Ni(dmit)2] (NMQ = N‐methylquinolinium, dmit = 1,3‐dithiol‐2‐thione‐4,5‐dithiolate) functions as a diamagnetic insulator with an activation energy Ea(dark) of 0.20 eV. However, at 300 K, it exhibits ca. 40 times higher conductivity (σUV) under UV irradiation [(375 ± 5) nm, 15.7 mW cm–2] than it does under dark conditions (σdark). The ratio σUV/σdark rapidly increases with decreasing temperature and reaches ca. 880 at 200 K. From the temperature dependence of σUV, the activation energy under irradiation Ea(UV) is 0.12 eV. These observations cannot be explained as the result of sample heating during UV irradiation. Rather, the X‐ray photoelectron spectra of the sulfur and nickel atoms, the calculated band structure, and the UV/Vis spectra of the salt can all be explained consistently as follows: charge transfer between the Ni(dmit)2 moieties upon exposure to 375 nm UV light induces melting of the charge‐ordered state and produces the unusually large photoconductivity of NMQ[Ni(dmit)2].

Metal Site Doping in the Narrow-Gap FeGa3 Semiconductor

The effects and feasibility of metal site doping of the tetragonal diamagnetic insulator FeGa3 by Fe/Co, Fe/Mn, and Co/Ni substitutions were investigated by the X-ray electron-probe microanalysis, electrical resistivity, specific heat, and magnetic susceptibility measurements. The substitution of Co for Fe in FeGa3 does not change its structural type and preserves the structure of the binary parent compound ( FeGa3), whereas the solubility of Mn in the FeGa3 -type structure is limited to 3 at.% and a finite solubility of Ni in CoGa3 is not detected.

Reversible iodine absorption by alkali-TCNQ salts with associated changes in physical properties

Alkali metal salts of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) reversibly absorb iodine forming the ternary salts M(TCNQ)I (M = Li, Na, K) and M2(TCNQ)3I2 (M = Rb). The ternary salts are also obtained by solid-state reactions of TCNQ with alkali iodides. These salts are paramagnetic and have high electrical conductivities, ∼10−1 S cm−1, for compacted pellets, whereas the alkali metal salts of TCNQ are diamagnetic insulators. The ternary salts further absorb iodine to give over-doped salts M(TCNQ)In (n ≈ 6, M = Na, K), which gradually release iodine to give M(TCNQ)I. In contrast, the solid-state reaction of F4TCNQ and sodium iodide produces Na(F4TCNQ), which does not exhibit iodine absorption.

Highly Spin-Polarized Conducting State at the Interface between Nonmagnetic Band Insulators:LaAlO3/FeS2(001)

First-principles density functional calculations demonstrate that a spin-polarized two-dimensional conducting state can be realized at the interface between two nonmagnetic band insulators. The (001) surface of the diamagnetic insulator FeS(2) (pyrite) supports a localized surface state deriving from Fe d orbitals near the conduction band minimum. The deposition of a few unit cells of the polar perovskite oxide LaAlO(3) leads to electron transfer into these surface bands, thereby creating a conducting interface. The occupation of these narrow bands leads to an exchange splitting between the spin subbands, yielding a highly spin-polarized conducting state distinct from the rest of the nonmagnetic, insulating bulk. Such an interface presents intriguing possibilities for spintronics applications.

Synthesis, magnetic and thermoelectric properties of Rh 2MO 6 (M = Mo, Te, and W) with rutile-related structure

The Rh 2MO 6 compounds with M = Mo, W and Te were synthesized by solid state reaction. The compounds all crystallize in a rutile-type structure. These compounds would be expected to be diamagnetic insulators if the oxidation states were Rh 3+ and M 6+. In fact, all show relatively high electronic conductivities with Rh 2TeO 6 showing the highest electronic conductivity of ∼500 S/cm at room temperature. Measurable magnetic moments also indicate valence degeneracy between Rh and the M cation. The measured Seebeck coefficients are relatively low and positive indicating hole-type conduction.

Transition from the diamagnetic insulator to ferromagnetic metal in [formula omitted

We have analyzed, using the theoretical GGA + U calculations, different configurations of spin states (low-spin, LS; intermediate-spin, IS and high-spin, HS Co 3 + ) and proposed a model that accounts for magnetic and electric transport properties of perovskite cobaltites upon doping by charge carriers. In particular, it appears that the compositional transition from the diamagnetic LS phase of LaCoO 3 to the ferromagnetic metallic IS phase in La 1 - x Sr x CoO 3 ( x > 0.2 ) involves the same mechanisms as the high-temperature transition in pure LaCoO 3 . The process occurs gradually via a phase-separated state, where metallic IS domains stabilized through a charge transfer between Co 4 + and Co 3 + neighbors coexist with the Co 4 + poor regions in the LS ground state (or at higher temperatures, in mixed LS/HS state). This phase separation vanishes when doping in La 1 - x Sr x CoO 3 reaches x ∼ 0.2 , and a uniform IS phase, analogous to that in pure LaCoO 3 in the high-temperature limit, is established.

Synthesis and structure of charge transfer salts of tetrathiafulvalene (TTF) and tetramethyl-TTF with 2,4,7-trinitro and 2,4,5,7-tetranitro-9-fluorenone

Charge transfer salts of tetrathiafulvalene (TTF) and tetramethyltetrathiafulvalene (TMTTF) with the organic acceptors 2,4,7-trinitro-9-fluorenone and 2,4,5,7-tetranitro-9-fluorenone have been prepared and characterized. The compounds (TTF)[TENF] ( 1), (TTF) 3[TRNF] 2 ( 2) and (TMTTF)[TRNF] ( 3) contain mixed stacks of alternating TTF and nitrofluorenone units. Surprisingly, the degree of charge transfer that occurs in these salts is not controlled solely by the redox potentials of the building blocks, but apparently also by the most effective intermolecular interactions in the solid, as determined from the crystal structures obtained. These three compounds exhibit poor electron delocalization and therefore they behave as diamagnetic insulators.

Magnetic alignment experiment of fine graphite-crystals dispersed in He gas oriented to study alignment of crystalline-axes of nano-sized non-magnetic particles

The ensemble of nano-sized crystals is expected to attain additional physical properties when preferential alignments of certain crystal-axes are achieved by a magnetic field. The reduction of temperature T may realize alignment even if the mole number of the particle N and the diamagnetic anisotropy per mole (Deltachi)(DIA) are considerably small for the nano-sized diamagnetic oxides, since alignment proceeds by the balance between the energy of rotational Brownian motion and field-induced anisotropy energy. Alignment of various basic inorganic oxides such as gypsum, quartz, forsterite, KDP or calcite, having a size of 20 nm diameter, is expected to occur by a field intensity of approximately 50 T at T = 10 K; this intensity is presently available at a high magnetic-field laboratory. It is expected that the magnetic alignment of nano-sized particles can be observed by dispersing the particles in He gas, as achieved recently for micron-sized graphite crystals; a cryogenic liquid cannot be used as a dispersing medium. Measured (Deltachi)(DIA) values accumulated for basic inorganic-oxides are explained quantitatively by assuming that individual bonding-orbital composing the material possesses a constant amount of diamagnetic anisotropy; hence the majority of diamagnetic nano-sized insulators are expected to show magnetic alignment at finite field intensity.

Zn(C 3H 3N 2) 2: a novel diamagnetic insulator

We have prepared polycrystalline samples of Zn(C 3H 3N 2) 2 by a liquid-mix technique. Characterization of the obtained samples has been performed with the aid of elemental, thermogravimetric, infrared spectra and X-ray powder diffraction analysis. We have measured electric permittivity ( ε′, ε″), ac-conductivity ( σ ac ), magnetic susceptibility ( χ) and specific heat ( C p ). The obtained data indicate that this material is a new diamagnetic insulator. A maximum around 4.5 K is found in C p T −3, and it is suggested that in addition to the Debye lattice contribution, there exists a low-frequency mode assigned as an Einstein mode contribution to the total specific heat. As a main result of the study, we found ε′ to be constant in a wide temperature range and to have a small value of 2.3 at room temperature. This feature in combination with other properties like crystallization, good thermal stability (up to 400°C), weak moisture sensitivity and simple synthesis makes Zn(C 3H 3N 2) 2 to be a promising candidate for good insulating material in various applications.

Interlayer Coupling in EuS-Based Superlattices (Dependence on the Energy Structure of Non-Magnetic Layer)

The interlayer coupling between ferromagnetic EuS layers separated by spacer layers of diamagnetic insulators, YbSe and SrS, is studied within a 3D tight-binding model. The dependencies of the coupling strength on the energy structure of the spacer, on strains resulting from the lattice mismatch between the superlattice constituents, as well as on an applied hydrostatic pressure and lattice deformations, are presented. The sign and the range of the obtained coupling agree with the behavior of magnetic correlations observed recently in neutron reflectivity spectra of EuS/YbSe superlattices.

Electronic structure and metal-insulator transition in SrTi 1 - x Ru xO 3

We studied the changes in the electronic structure of SrTi1-xRuxO3 across the metal-insulator transition. The parent compound, SrTiO3, is a well known diamagnetic insulator; whereas the doped compound, SrTi1-xRuxO3, becomes a ferromagnetic metal above x C = 0.35. The techniques used in the study were photoemission (PES) and O 1 s X-ray absorption (XAS) spectroscopy. The experimental spectra were analyzed in terms of band structure and Hubbard model calculations. The PES and XAS spectra of SrTi1-xRuxO3 show the Ru 4 d bands growing in the band gap of SrTiO3 . The analysis in terms of the Hubbard model indicates that the Ti 3 d and Ru 4 d bands are mostly decoupled. This suggests that the metal-insulator transition is a percolation transition like that of metals embedded in a rare gas matrix. Electron correlation effects are present in this system, but they do not seem to play a major role in the transition.

Symmetry crossover and excitation thresholds at the neutral-ionic transition of the modified Hubbard model

Exact ground states, charge densities, and excitation energies are found using valence bond methods for N-site modified Hubbard models with uniform spacing. At the neutral-ionic transition (NIT), the ground state has a symmetry crossover in $4n$ and $4n+2$ rings with periodic and antiperiodic boundary conditions, respectively. Large site energies $\ensuremath{\Delta}$ stabilize a paired state of the half-filled chain, while large U stabilizes a covalent state. Finite-transfer integrals t shift the NIT to the covalent side of $U\ensuremath{-}2\ensuremath{\Delta}.$ Exact results to $N=16$ in the full basis and to $N=22$ in a restricted basis for large U and $\ensuremath{\Delta}$ are extrapolated to obtain the crossover and charge density of extended chains. The modified Hubbard model has a continuous NIT between a diamagnetic band insulator on the paired side and a paramagnetic Mott insulator on the covalent side. The singlet-triplet (ST), singlet-singlet (SS), and charge gaps for finite N indicate that the ST and SS gaps close at the NIT with increasing U, and that the charge gap vanishes only there. Finite-N excitations constrain all singularities to $\ifmmode\pm\else\textpm\fi{}0.1t$ of the symmetry crossover. The NIT is interpreted as a localized ground state (GS) with finite gaps on the paired side and an extended GS with vanishing ST and SS gaps on the covalent side. The charge gap and charge stiffness indicate a metallic GS at the transition that, however, is unconditionally unstable to dimerization. Finite $\ensuremath{\Delta}$ breaks electron-hole $(e\ensuremath{-}h)$ symmetry, but the modified Hubbard model has an extended $e\ensuremath{-}h$ symmetry, and a strong mixing of spin and charge excitations is limited to a few t's about the NIT. Exact finite-size results complement other approaches to valence or ferroelectric transitions in organic charge-transfer salts or in inorganic oxides, and to electron-vibration coupling and structural instabilities in one-dimensional systems.