A study of the new compound YBa4Fe3O11−y

The compound YBa₄Fe₃O _y was synthesized where the Fe atoms completely substituted for the Cu atoms in YBa₄Fe₃O _y . The X-ray phase analysis of the synthesized material showed that the diffraction pattern corresponds to the data for the compound YBa₄Fe₃O _y .⁵⁷Fe Mössbauer measurements of the compound were performed at room temperature after different heat treatments: high-temperature synthesis in an oxygen atmosphere and in air, and low-temperature annealing in oxygen and in vacuum. No magnetic components are observed after any heat treatments. The Fe atoms in the compound have two valence states, Fe³⁺ and Fe⁴⁺. The idealized model of the 1-4-3 Fe structure is discussed.     

X-ray photoelectron spectroscopy characterization of the layered intercalated compound K2xMn1 − xPS3

Polycrystalline powders of the layered MnPS₃ compound have been intercalated with K⁺ ions by ion-exchange to yield the K_2xMn_1 − xPS₃ intercalate. X-ray photoelectron spectroscopy has been applied to learn about the electronic structure of this compound. In particular, we have studied the XPS spectra of the Mn 2p and 3p, P and S 2p, K 2p and 3p core levels and of the valence band region. The binding energies for various core levels of the elements present in this compound and their observed chemical shifts are analyzed. The data give evidence for the lack of non-equivalent atoms of K, Mn, P and S. Shake-up satellites are present at the Mn 2p and 3p core levels. The occurrence of such lines allows us to hypothesize that K_2xMn_1 − xPS₃ is a large-gap insulating Mn compound. Confirmation that only an ion transfer accompanies the intercalation process is given from both the strong observed similarity with the corresponding XPS spectra in MnPS₃ and the observed binding energy positions of the K 2p and 3p levels. As regards the valence band XPS spectrum, the observed analogies with the corresponding XPS spectra of the pure compound and of other K compounds have allowed us to single out two regions and their probable contributors.     

Magnetic structure of the Nd5Ge3 compound

Neutron diffraction measurements of the Nd₅Ge₃ intermetallic compound with a hexagonal structure (space group P6₃/mcm) have been performed at temperatures of ～10 and 293 K. The basis functions of irreducible representations of the space group D _6h ³ (P6₃/mcm), which are calculated as a result of the symmetry analysis of possible magnetic structures with the wave vector k = μb ₁, are used to facilitate the search for a real model of the magnetic structure of the compound.     

Analysis of nonlinearity of magnetization of YBa2Cu3O7 − x by the magnetic field modulation method

Temperature dependences of the magnetization harmonics of YBa₂Cu₃O_{7 ? x} monodomain samples are studied experimentally at temperatures of 77–120 K. It is found that nonlinearity of magnetization of YBa₂Cu₃O_{7 ? x} (higher harmonics generation) is observed up to temperatures T = 103–112 K, which are much higher than the superconducting transition temperature of this compound. At the same temperatures, the temperature dependence of resistivity begins to deviate from linearity. The observed singularity of the magnetization of YBa₂Cu₃O_{7 ? x} is associated with the emergence of a pseudogap state in this compound.     

Synthesis and characterization of CaLaFe11O19

A new ferrimagnetic compound with the chemical formula CaLaFe₁₁O₁₉ has been synthesized by solid state reaction between the respective oxides and their structural, electrical and magnetic properties have been studied. One magnetic Fe³⁺ ion in CaLaFe₁₂O₁₉ is replaced by La³⁺ ion. The crystallographic results show the compound is hexagonal magnetoplumbite. The electrical conductivity has been measured from 300 to 800 K. The activation energy changes at Curie temperature (653 K). The compound is ferrimagnetic from 300 to 653 K and above T_c it acts as a paramagnetic. Variation of inverse molar susceptibility has been measured at various temperature in paramagnetic region and Curie molar constant (C_m) is calculated. AC susceptibility measurements are made at room temperature. The Seebeck coefficient (S) measurements show that the compound is n-type.     

Magnetism in UNi2Ga3

We present the physical properties of the new intermetallic compound UNi₂Ga₃. This compound crystallizes in the hexagonal CaCu₅-structure, and bulk experiments (specific heat c _p, susceptibility X, magnetization M and resistivity ρ) indicate the system to undergo a magnetic transition at 9.5 K. No superconductivity is observed down to 50 mK. The magnetic transition in UNi₂Ga₃ closely resembles that of the incommensurably ordered state in the related heavy-fermion superconductor UNi₂Al₃. In addition, and independently from the conditions for sample preparation, we found indications for a considerable degree of lattice disorder, likely due to structural Ga/Ni disorder. We discuss our results, particularly the absence of superconductivity in UNi₂Ga₃, in comparison to UNi₂Al₃.     

Symmetric logarithmic heat capacity anomaly of the layered manganese compound: Mn(NH3)2Ni(CN)42C12H10

The magnetic susceptibility and the heat capacity of a layered manganese compound Mn(NH₃)₂Ni(CN)₄2C₁₂H₁₀ have been measured down to the antiferromagnetic ordered state. A similar symmetric logarithmic singularity in the heat capacity is found for the isomorphic nickel compound Ni(NH₃)₂Ni(CN)₄2C₁₂H₁₀ has been observed at T_N = 0.172 K.     

Specific features of the crystal structure and magnetic properties of the DyFeTi2O7 compound

Results of studying the specific features of formation of the crystal structure and distribution of iron cations over the sites in the DyFeTi₂O₇ compound have been presented and the comparison with the GdGaTi₂O₇ isostructural compound has been performed. The atomic disorder in the distribution of the Fe³⁺ ions over structural sites in the DyFeTi₂O₇ compound is confirmed by the Mössbauer spectroscopy and X-ray diffractometry. The results of magnetic measurements in the low-temperature region have revealed an inflection point in the temperature dependence of the magnetic moment and its dependence on the magnetic prehistory of the sample. The obtained experimental data suggest that there is a spin glass state with freezing point T _f = 6 K in the DyFeTi₂O₇ compound.     

Structure relations in the x-ray photoelectron spectra of three chromium compounds

The chemical shift in electron binding energy, magnetic splitting of electron shells, and structures in the valence band are examined for chromium in the 3 + and 6 + oxidation states.The splitting of the Cr 3s energy level is associated with the appearance of a sharp Cr 3d line in the valence band. The relative chemical shift in the Cr 2p_{$\text{3}\text{2}$} line between Cr₂O₃ and K₂Cr₂O₇ is verified in the mixed compound KCr₃O₈ which contains both types of Cr ions, and the structure of this compound is verified by the X-ray photoelectron spectra. The spin-orbit intensity ratio of the 2p doublet of Cr⁶⁺ is 3, instead of the theoretical value of 2, and the spin-orbit splitting is less than for Cr³⁺. In the 3p level of Cr the relative chemical shift is 3.5 eV whereas for the 2p_{$\text{3}\text{2}$} level the shift is only 2.4 eV. The differences in chemical shift and intensity ratio can not be explained.     

Neutron diffraction study of DyCu2Ge2

The DyCu₂Ge₂ compound was studied by neutron diffraction on the Grenoble Nuclear Research Center multicounter system. The compound is isostructural to the rare earth RCu₂Ge₂ compounds with space group I4/mmm. 19 superlattice lines were observed in the 3 K pattern which are consistent with a doubling of the unit cell in the a and c directions. The moment value is 8 μ_B making an angle of 30° with a and 70° with c axis. The structure consists of ferromagnetic (1 0 1) layers with antiferromagnetic coupling between them. The Néel and Curie paramagnetic temperature of this compound is 8 K and ? 15 K respectively.     

New Fe-based amorphous compound powder cores with superior DC-bias properties and low loss characteristics

The Fe–Si–B–P–C metallic glassy alloys exhibit relatively high glass forming ability (GFA) as well as good soft magnetic properties such as ultra-low core loss. In this paper, the metallic glassy alloy (Fe_0.76Si_0.09B_0.10P_0.05)₉₈C₂ has been newly developed. A new Fe-based amorphous compound powder was prepared from FeSiB amorphous powder by crushing the amorphous ribbons as the first magnetic component and FeSiBPC metallic glassy powder by water atomization as the second magnetic component. Subsequently by adding organic and inorganic binders to the compound powder and cold pressing, the new Fe-based amorphous compound powder cores were fabricated. These new Fe-based amorphous compound powder cores combine the superior DC-bias properties and the excellently low core loss. The core loss of 453 kW/m³ at B_m=0.1 T and f=100 kHz was obtained when the mass ratio of FeSiB/FeSiBPC equals 3:2, and meanwhile the DC-bias properties of the new Fe-based amorphous compound powder cores just increased by 10% at H=100 Oe for μ=60 compared to those of the FeSiBPC powder cores. In addition, with the increase in the content of the FeSiPC metallic glassy powder, the core loss tends to decrease.     

157 T internal magnetic field in Fe[C(SiMe3)3]2 compound at 20 K

Fe[C(SiMe₃)₃]₂ compound, in which iron is coordinated by two carbons, was prepared using the reaction of FeCl₂ with (Me₃Si)₃CLi, and investigated by XRD, ⁵⁷Fe Mössbauer spectroscopy and DFT calculations. 157.5 T hyperfine magnetic field was found at the site of the iron nucleus of this compound at 20 K. DFT calculations predict the quintet states to be clearly favored energetically over the lower spin states. The population analysis reveals considerable 4s as well as large unpaired 3d electron contributions, which can be responsible for the extremely high hyperfine field.     

Structure of intercalation compound Ag<Subscript>0.25</Subscript>ZrSe<Subscript>2</Subscript>

The structure of intercalation compound Ag-ZrSe₂ has been investigated. The matrix compound ZrSe₂ and intercalated phase Ag_0.25ZrSe₂ belong to the trigonal system (sp. gr. P-3m1). The lattice parameters of these phases are refined.     

Triplet exciton in a non-reactive bis-triphenyllead (or tin) diacetylene crystal. A spectroscopic study

The lowest triplet exciton state of crystals formed by (C₆H₅)₃?X?C ≡ C?C ≡ C?X?(C₆H₅)₃ where X is Pb or Sn and an equimolecular amount of CH₂Cl₂ solvent molecules, is studied through the analysis of absorption and of phosphorescence emission and excitation spectra at low temperatures. In the lead compound, the origins of absorption and emission are identical, showing the dominance of free exciton emission and the absence of crystal lattice relaxation in the excited state; the splitting is accounted for by symmetry considerations in the different crystalline phases; the triplet exciton band is several cm^-1 wide, although the nearest diacetylene-diacetylene distance is about 10 Å. There is evidence for triplet exciton motion, through the detection of trap (presumably X-trap) emission in the tin compound, and through the analysis of the excitation spectrum lineshape, showing the effect of exciton-exciton interaction in the lead compound.     

Band structure and the magnetic and elastic properties of SrFeO<Subscript>3</Subscript> and LaFeO<Subscript>3</Subscript> perovskites

The band structure and the magnetic and elastic characteristics of SrFeO₃ and LaFeO₃ perovskites with ferromagnetic and antiferromagnetic collinear spin configurations (of the A, C, and G types) are investigated using the ab initio pseudopotential method (the VASP program package) with the inclusion of the single-site Coulomb correlations (the LSDA + U formalism). It is shown that, in the pressure range 0–50 GPa, the most stable states are the ferromagnetic metal state for the SrFeO₃ compound and the antiferromagnetic insulator state of the G type for the LaFeO₃ compound.     

High-temperature heat capacity of TbFe3(BO3)4

The molar heat capacity of TbFe₃(BO₃)₄ in the temperature range of 346–1041 K has been measured by differential scanning calorimetry. It has been found that the C _p = f(T) curve does not show extremes. The thermodynamic properties of the oxide compound have been determined from the experimental data.     

Structure,electrical transport,and optical properties of a new ordered iron intercalated dichalcogenide,Fe0.34TiSe2

The compound Fe_0.34TiSe₂ crystallizes in space group D³_3d?P3&#x0304;ml of the trigonal system with 8 formula units in a cell of dimensions a = 7.148(4), c = 11.880(7) Å at 117 K. The structure of Fe_0.34TiSe₂ can be derived from that of TiSe₂ by insertion of Fe atoms into some of the octahedral holes between the layers. No two adjacent octahedral holes along c contain Fe atoms, that is no two Fe atoms are related by a translation of $\text{c}\text{2}$. The compound Fe_xTiSe₂, x = 0.34, exhibits physical properties remarkably different from those found in either the host material, TiSe₂, or in low iron concentration (x < 0.2) intercalated materials. The electrical resistivity of this compound exhibits a sharp decrease below 120 K which is coincident with a well defined peak in the Hall coefficient. These data have been interpreted as the onset of antiferromagnetic ordering as suggested by results of magnetic susceptibility measurements. Optical reflectance measurements indicate a simple Drude-like free carrier behavior and are consistent with the interpretation of iron as an electron donor in this material.     

The crystal structures of the ion conductors (NH+4)Zr2(PO4)3and (H3O+)Zr2(PO4)3

The crystal structures of (NH⁺₄)Zr₂(PO₄)₃ and (H₃O⁺)Zr₂(PO₄)₃ have been determined from neutron time-of-flight powder diffraction data obtained at 15 K. Both compounds are rhombohedral, $\text{R}\text{3}\text{c}$, with cell parameters a=8.7088(1) and c=24.2197(4) Å for the ammonium compound and a=8.7528(2), c=23.6833(11) Å for the hydronium compound. In both cases the ions are completely localized in the type I cavities and hydrogen bonded to lattice oxygens. The measured unit cell parameters are relatively large for this class of compounds but the entrance ways into the cavities are still too small to allow for unrestricted movement of the ions. Thus the low conductivity of the hydronium ion is related to this and other structural features.     

Cluster glass magnetism in the phase-separated Nd2/3Ca1/3MnO3 perovskite

A detailed study of the low-temperature magnetic state and the relaxation in the phase-separated colossal magnetoresistance Nd_2/3Ca_1/3MnO₃ perovskite has been carried out. Clear experimental evidence of the cluster-glass magnetic behavior of this compound has been revealed. Well defined maxima in the in-phase linear ac susceptibility χ′(T) were observed, indicative of the magnetic glass transition at T_g∼60 K. Strongly divergent zero-field-cooled and field-cooled static magnetizations and frequency dependent ac susceptibility are evident of the glassy-like magnetic state of the compound at low temperatures. The frequency dependence of the cusp temperature T_max of the χ′(T) susceptibility was found to follow the critical slowing down mechanism. The Cole–Cole analysis of the dynamic susceptibility at low temperature has shown extremely broad distribution of relaxation times, indicating that spins are frozen at “macroscopic” time scale. Slow relaxation in the zero-field-cooled magnetization has been experimentally revealed. The obtained results do not agree with a canonical spin-glass state and indicate a cluster glass magnetic state of the compound below T_g, associated with its antiferromagnetic–ferromagnetic nano-phase segregated state. It was found that the relaxation mechanisms below the cluster glass freezing temperature T_g and above it are strongly different. Magnetic field up to about μ₀H∼0.4 T suppresses the glassy magnetic state of the compound.     

Systematic investigations on the magnetic properties of Gd3Ni2In4 compound

We have investigated the structural, magnetic, magnetocaloric, thermodynamic and transport properties of polycrystalline Gd₃Ni₂In₄ compound. X-ray powder diffraction pattern shows that Gd₃Ni₂In₄ crystallizes in hexagonal Lu₃Co₂In₄ – type structure. Magnetization studies reveal the presence of two magnetic transitions, T_N and T_C at 21 K and 55.5 K, respectively. The maximal value of magnetic entropy change, -ΔS_M, computed from isothermal magnetization data in a magnetic field of 9 T is 4.57 J/kg K, which is spread over a wide temperature (ΔT = 61.5 K) and hence yields a relative cooling power (RCP) of 281 J/kg. In addition, the compound shows a significant positive magnetoresistance, MR (T = 2 K) = 44% in B = 9 T. These results on Gd₃Ni₂In₄ compound signify that such materials exhibiting successive reversible magnetic transitions may comprise a distinct class of magnetocaloric materials as they work in a wider temperature range than conventional refrigerant materials.