The <Superscript>57</Superscript>Fe hyperfine interactions in the iron-bearing phases in some LL ordinary chondrites

The study of several LL ordinary chondrites such as NWA 6286 LL6, NWA 7857 LL6 and Chelyabinsk LL5 fragments with different lithology was carried out using scanning electron microscopy with energy dispersion spectroscopy, X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy with a high velocity resolution at 295 K. Small variations in the ⁵⁷Fe hyperfine parameters were revealed for the M1 and M2 sites in olivine, orthopyroxene and clinopyroxene as well as for α-Fe(Ni, Co), α ₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases, and for troilite in different samples of studied LL ordinary chondrites.     

Electron mass enhancement and magnetic phase separation near the Mott transition in double-layer ruthenates

We present a detailed investigation of the specific heat of Ca₃(Ru_1-xM_x)₂O₇ (M = Ti, Fe, Mn) single crystals. Depending on the dopant and doping level, three distinct regions are present: a quasitwo-dimensional metallic state with antiferromagnetic (AFM) order formed by ferromagnetic bilayers (AFM-b), a Mott insulating state with G-type AFM order (G-AFM), and a localized state with a mixed AFM-b and G-AFM phase. Our specific heat data provide deep insights into the Mott transitions induced by Ti and Mn doping. We observed not only an anomalous large mass enhancement, but also an additional term in the specific heat, i.e., C ∝ T², in the localized region. The C ∝ T² term is most likely due to long-wavelength excitations with both FM and AFM components. A decrease in the Debye temperature is observed in the G-type AFM region, indicating lattice softening associated with the Mott transition.     

Comparative study of Aliskerovo,Anyujskij, Sikhote-Alin and Sterlitamak iron meteorites using Mössbauer spectroscopy

A comparative study of Sikhote-Alin IIAB, Anyujskij IIAB, Aliskerovo IIIE-an and Sterlitamak IIIAB iron meteorites was carried out using Mössbauer spectroscopy with a high velocity resolution as well as using metallography, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. Different numbers of spectral components were found in the Mössbauer spectra of Sikhote-Alin IIAB and Anyujskij IIAB and in the spectra of Aliskerovo IIIE-an and Sterlitamak IIIAB iron meteorites. The values of hyperfine field at the ⁵⁷Fe nuclei obtained for spectral components were related to α-Fe(Ni, Co), α ₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases with variations in Ni concentration.     

Features of Electronic Structure of Intermetallic Compounds CeNi<Subscript>4</Subscript>M (M = Fe,Co, Ni,Cu)

The evolution of the electronic structure of CeNi₄M (M = Fe, Co, Ni, Cu) intermetallics depending on the type of nickel substitutional impurity is explored. We have calculated band structures of these compounds and considered options of substituting one atom in nickel 3d sublattice in both types of crystallographic positions: 2c and 3g. The analysis of total energy self-consistent calculations has shown that positions of 2c type are more energetically advantageous for single iron and cobalt impurities, whereas a position of 3g type is better for a copper impurity. The Cu substitutional impurity does not change either the nonmagnetic state of ions or the total density at the Fermi level states. Fe and Co impurities, on the contrary, due to their considerable magnetic moments, induce magnetization of 3d states of nickel and cause significant changes in the electronic state density at the Fermi level.     

Correlation between the optical properties of surface layers and bulk characteristics of amorphous alloys

Spectral ellipsometry was used to study surface layers of Fe₈₀ A ₅B₁₅ (A = Ti, V, Cr, Mn, Fe, Co, Ni) and Fe_78-x Ni_xSi₉B₁₃ (x = 0, 1, 4, 8, 16, 21 at. %) amorphous metal alloys obtained by melt spinning. The optical characteristics of the alloys were determined by solving the inverse problem of ellipsometry. A correlation between the optical properties of the surface layers of amorphous alloys and their thermal stability was found.     

Re-examination of Dronino iron meteorite and its weathering products using Mössbauer spectroscopy with a high velocity resolution

Re-examination of Dronino iron meteorite and products of its weathering in the internal and external surface layers was carried out using Mössbauer spectroscopy with a high velocity resolution. New results showed the presence of α-Fe(Ni, Co), α ₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases with variations in Ni concentration in Dronino metallic iron alloy. The surface weathering products were supposed as magnetite and/or maghemite, goethite with different particles size and probably ferrihydrite in the internal layer and goethite with different particles size and probably ferrihydrite in the external layer.     

Investigation of the cation distribution in perovskite-like oxides with Mössbauer spectroscopy

Complex perovskite-like oxides, such as LnFe_2/3Mo_1/3O₃ orthoferrites, Ln_8?ySr_yCu_8?xFe_xO₂₀ (8-8-20), Pr₄BaCu₄FeO_13-δ(4-1-5), YBa_2-yLa _y Cu_3-xFe _x O_7-δ and Y_1-yCa _y Ba _y La _y Cu_3-xFe _x O_7-δ (1-2-3), are studied by means of Mössbauer spectroscopy. At room temperature, the spectra of the orthoferrites contain only magnetic components. The spectra of the 1-2-3 compounds contain only magnetically disordered components: iron atoms substitute for copper at Cu(1) sites, taking various configurations: planar squares, quadratic pyramids, and octahedra. Cuprates 8-8-20 and 4-1-5 have a wide diversity of spectra. In the 8-8-20 oxides, a phase related to the pyramidal environment of the iron cations is present at any iron concentration. In all the perovskites, iron cations become magnetically ordered only at octahedral sites of the structure.     

Hall effect in the Ce(Al<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript> heavy-fermion system

The influence of substitution on the binding energy of many-body states and the formation of the magnetically ordered state in a heavy-fermion compound (CeAl₂) have been studied by measuring the transport characteristics (Hall effect, resistivity) in intermetallic compounds of the Ce(Al_1?x M _x )₂ system (M = Ni, Co; x ≤ 0.08). It is established that the Hall coefficient R _H in Ce(Al_1?x Co _x )₂ intermetallides with x = 0.05 and 0.08 grows by more than an order of magnitude as the temperature decreases from 1.8 to 300 K. The experimental data are used to estimate the effective mass of charge carriers, the relaxation time, and the localization radius of many-body states.     

Intrinsic and Zn-, Ce-, Tb-, Er-, Sm-, and Eu-Activated photoluminescence of pseudoamorphous GaN and InGaN thin films

Thin films of pseudoamorphous GaN (a-nc-GaN), as well as of its alloys with indium, In_xGa_1−x N (x=0.04, 0.16), were prepared by magnetron sputtering of a metallic target in the plasma of a reactive nitrogen and argon mixture. The a-nc-GaN films were codoped by the Zn acceptor impurity and a set of rare-earth metal (REM) dopants, namely, Ce, Tb, Er, Sm, and Eu. Photoluminescence (PL) spectra excited by a nitrogen laser with wavelength λ=337 nm at room temperature and 77 K were measured for all compositions and a set of impurities. It was shown that the high-energy PL edge of the pseudoamorphous (a-nc) GaN matrix lies at the same energy as that of the crystalline (epitaxial) c-GaN. As in c-GaN, the Zn acceptor impurity stimulates blue luminescence; however, the PL spectrum is substantially more diffuse, with practically no temperature quenching of the PL present. Indium doping in an amount of 16 at. % results in strong PL with a diffuse peak at 2.1–2.2 eV; the PL of the alloy exhibits temperature quenching as high as a factor of three to four in the interval 77–300 K. The decay time of the PL response increases up to 50 μs. RE impurities enter the amorphous GaN host as trivalent ions and produce narrow-band (except Ce) high-intensity spectra, thus indicating both a high solubility of RE impurities in a-nc-GaN and the generation of an effective crystal field (by the GaN anion sublattice) whose local symmetry makes the intracenter f-f transitions partly allowed. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 3, 2003, pp. 395–402. Original Russian Text Copyright ? 2003 by Andreev.     

Electronic structure of the Np<Emphasis Type="Italic">MT</Emphasis> <Subscript>5</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Fe,Co, Ni; <Emphasis Type="Italic">T</Emphasis> = Ga,In) series of neptunium compounds

Evolution of the electronic structure of the NpMGa₅ (M = Fe, Co, Ni) series of neptunium compounds, whose crystal structure is similar to that of the known family of Pu115 superconductors, was studied by the LDA + U + SO method. The calculations took into account both the strong electron correlations and the spin?orbit coupling in the 5f shell of neptunium. For the first time, the electronic structure was calculated for a hypothetical series of compounds in which gallium is replaced with indium. Parameters of the crystal structure of the given series were obtained using the relationship between the parameters of the crystal structure of the earlier-studied compounds PuCoGa₅ and PuCoIn₅. The analysis of the electronic structure and characteristics of neptunium ions calculated in the framework of the LDA + U + SO method showed that the neptunium ions in NpMIn₅ with M = Fe, Co, and Ni should have an electron configuration closer to f⁴, but a spin and magnetic characteristics close to those in NpMGa₅.     

Low-temperature heat capacity upon the transition from paramagnetic to ferromagnetic Heusler alloys Fe<Subscript>2</Subscript> <Emphasis Type="Italic">Me</Emphasis>Al (<Emphasis Type="Italic">Me</Emphasis> = Ti,V, Cr,Mn, Fe,Co, Ni)

The heat capacity of band magnets Fe₂MeAl (Me = Ti, V, Cr, Mn, Fe, Co, Ni) ordered in crystal structure L2₁ has been measured in the range 2 K ≤ T ≤ 50 K. The dependences of the Debye temperature Θ_D, the Sommerfeld coefficient γ, and the temperature-independent contribution to heat capacity C₀ on the number of valence electrons z in the alloys have been determined.     

Equilibrium magnetic and orbital states of the manganites with four manganese atoms in the unit cell

The carrier energy spectrum and the total energy of various magnetic and orbital crystal-structure configurations of the manganites R _1?x A _xMnO₃ (R=La, Pr, Nd, Sm, etc.; A=Ca, Sr, Ba) with four manganese atoms in the unit cell have been calculated for the electron doping region x>0.5. The equilibrium magnetic and orbital configurations of the model are determined by minimizing the total energy of the system with respect to the angles θ _i ^s , φ_i, and θ _i ^o , which define the directions of the local manganese magnetic moments and the type of orbital mixing of the e _g electrons in the manganites. Assuming the parameters of the Heisenberg exchange interaction to be 0.018t<J _AFM<0.022t, the Hund exchange interaction to be J _H=2.5t, and the Jahn-Teller splitting to be Δ=1.5ty, the model with four manganese atoms in the unit cell predicts the experimentally observed magnetic phase alternation sequence G-C-A with increasing doping level y=1?x. For the values J _AFM<0.018t and y<0.28, this model allows the existence of a collinear phase H not observed earlier.     

Ab initio study of magnetic properties in the adsorption of transition-metal atoms on arsenene

The magnetic properties of adsorption of different transition-metal (TM) atoms (Co, Cu, Mn, Fe, and Ni) on arsenene are investigated using density functional theory (DFT). Magnetism appears in the cases of Co, Mn, and Fe. Among all the magnetic cases, the TM atom prefers the same adsorption site. Then, we further study the interaction in two-TM-adsorbed system and different magnetic states are observed. Our results show that both nonmagnetic and ferromagnetic states exist in two-Co-adsorbed system and the p-d hybridization mechanism results in its ferromagnetic state. However, for two Mn and two Fe adsorbed systems, an AFM interaction is found, which could be reasonably explained by the superexchange mechanism. Such multiple magnetic properties may suggest promising applications of TM-adsorbed arsenene in the future.     

New data on the mechanism of decay of the giant dipole resonance in the <Superscript>58</Superscript>Ni nucleus

New data on the mechanism of decay of the giant dipole resonance in the ⁵⁸Ni nucleus are obtained from an analysis of the experimental cross sections for the photonucleon reactions ⁵⁸Ni(γ, p_i)⁵⁷Co and ⁵⁸Ni(γ, n_i)⁵⁷Ni. The method used in this analysis takes into account both the energy spread of the dipole strength concentrated in various isospin components of the giant dipole resonance and the spread of the spectroscopic strength of the populated nucleon-hole states over the levels of the final nuclei. The entire body of experimental spectroscopic information about the levels of the final nuclei ⁵⁷Co and ⁵⁷Ni is employed. It is found that the probability of the semidirect mechanism of decay of the giant dipole resonance in the ⁵⁷Ni nucleus lies in the range 0.16–0.3. The probability of semidirect processes is much higher in the (γ, n) channel (0.28–0.62) than in the (γ, p) channel (0.07–0.17).     

The role of local environment in charge ordering of perovskite-like oxides

The properties of magnetically diluted perovskite-like complex oxides La_{2 ? x} A _x MO₄ (M is Fe or Mn and A is Sr or Ba) have been studied. Charge and spin ordering is suggested to be interrelated with the local structural characteristics and the electronic structure of nanoclusters of transition elements found in the ceramics studied.     

Oscillations of superconducting transition temperature in strong ferromagnet-superconductor bilayers

The superconducting transition temperature T _c of a “clean ferromagnet-dirty superconductor” bilayer is calculated using boundary conditions derived for the quasiclassical Green’s function. This combination corresponds to the majority of experiments, in which Fe, Ni, Co, or Gd are used as a material for the ferromagnetic layer. It is shown that T _c oscillates upon changing thickness of the ferromagnetic layer, in accordance with the experimental observations.     

Formation of nickel magnetic nanoparticles and modification of nickel phthalocyanine matrix by sodium doping

Data for the vapor-phase doping (300°C) of nickel phthalocyanine (NiPc) by sodium taken in different concentrations (x), as well as structural analysis data for Na _{x = 0.2}NiPc, Na _{x = 1}NiPc, and Na _{x = 3}NiPc samples, have been reported. The structure of the samples and their atomic configuration versus the doping level have been studied by transmission electron microscopy, Raman scattering, X-ray diffraction, X-ray absorption spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The structural parameters of Ni–N, Ni–C, and Ni–Ni bonds have been determined, and it has been found that, at a low level of doping by sodium, local structural distortions are observed in some molecules of the NiPc matrix near nickel atoms. The fraction of these molecules grows as the doping level rises from x = 0.2 to x = 1.0. It has been shown that doping changes the oscillation mode of light atoms, which indicates a rise in the electron concentration on five- and six-membered rings. At a high level of sodium doping (x = 3.0), nickel nanoparticles with a mean size of 20 nm and molecule decomposition products have been observed in the NiPc matrix. It has been found that the fraction of nickel atoms in the Na _{x = 3}NiPc nanoparticles as estimated from EXAFS data is sufficient for the room-temperature magnetic properties of the samples to persist for a long time.     

The spin cut-off factor for60Co

Nine experimental isomeric cross-section ratios for the reactions⁵⁹Co(n, γ)⁶⁰Co,⁶⁰Ni(n,p)⁶⁰Co, and⁶³Cu(n,α)⁶⁰Co are analysed in terms of statistical theory by means of the method ofHuizenga andVandenbosch. Theγ-cascades are treated by a new model which was recently published. The results confirm the energy dependence of the spin cut-off factor for⁶⁰Coσ～U^1/4 which should not be neglected. As a mean value (σ=4.3±0.3 is obtained forU=B _n =7.5 MeV in good agreement with a nuclear moment of inertia for a rigid sphere.     

Untersuchung gestörter Winkelverteilungen an F19 in ferromagnetischen Gittern

The perturbation of the 197 keV transition angular distribution in F¹⁹ was investigated by time-dependent spin rotation measurements following excitation with a pulsed beam. The recoil implantation technique was used to determine the internal magnetic fields for F¹⁹ in Fe, Co and Ni lattices. The results are:H _HF(F¹⁹ in Fe)=+(95700±500) Oe,H _HF(F¹⁹ in Co)=+(59500±1500) Oe,H _HF(F¹⁹ in Ni)=?(21830±350)Oe. The temperature and field dependence of the effective fields was studied. Strong satellite fields due to lattice perturbations were detected. The half life and the gyromagnetic ratio of the 197 keV 5/2⁺ state in F¹⁹ were redetermined asT _1/2=(80.2±0.5) nsec andg=+1.436±0.007.     

Mössbauer spectroscopy of H,L and LL ordinary chondrites

Fifteen fragments of H, L and LL ordinary chondrites were studied using Mössbauer spectroscopy with a high velocity resolution at 295 K. A new approach to fit troilite magnetic sextet using simulation of the full static Hamiltonian was applied that decreased spectra misfits. This approach permitted to obtain more correct and reliable parameters for the minor spectral components. Small variations in the ⁵⁷Fe hyperfine parameters were revealed for the M1 and M2 sites in both olivine and orthopyroxene as well as for α-Fe(Ni, Co), α ₂-Fe(Ni, Co) and γ-Fe(Ni, Co) phases in different ordinary chondrites. Some Mössbauer parameters showed the possibility to distinguish ordinary chondrites from H, L and LL groups that may be useful for their systematics.