We present magnetic and electrical transport properties such as resistivity, magnetoresistance, dielectric, and polarization of polycrystalline YbFe2O4. The ferrimagnetic transition temperature is measured at 243 K, followed by the two low-temperature transitions at similar to 190 and similar to 65 K, respectively. The magnetic properties including the M-H hysteresis loops exhibit a strong temperature dependence and possibly indicate a spin-glass state below 65 K for YbFe2O4. The iron Mossbauer measurement at 295 K confirms the presence of two Fe sites. The measured resistivity can be modeled with the Mott's variable-range hopping model, rho proportional to exp(T-0/T)(1/4), indicating the electron hopping between Fe2+ and Fe3+ sites. The magnetoresistance effects up to 6% at 8 T were observed and the effects could be caused by the field-induced changes in the electron-hopping processes. The frequency-dependent complex dielectric constant has been found to be strongly influenced by the contact effects, and the polarization of polycrystalline YbFe2O4 does not show ferroelectricity.

We present structural, magnetoresistance, magnetic, Mössbauer, and dielectric properties of polycrystalline LuFe2O4 prepared by an electron-beam assisted solid state reaction. The x-ray diffraction pattern shows the single phase LuFe2O4 sample, and the ferrimagnetic transition temperature is measured at 240 K, followed by the two low-temperature transitions at 210 K and 140 K, respectively. The magnetic properties including the M-H hysteresis loops exhibit a strong temperature dependence and possibly indicate that LuFe2O4 enters a spin-glass state below 100 K. The iron Mössbauer measurement at 300 K indicates two Fe sites. The resistivity follows Mott’s variable-range hopping model, ρ∝exp(T0/T)1/4, indicating the electron hopping between Fe2+ and Fe3+. The magnetoresistance effects up to 2.5% at 5 T in the ferrimagnetic state were observed, and the effects could be caused by the field-induced changes in the electron hopping processes. The frequency-dependent complex dielectric constant has been found to be strongly influenced by the contact effects, and the intrinsic ferroelectricity of LuFe2O4 could not be ascertained.

The basic oxygen furnace (BOF) slag use as raw material for cement production carries economic, environmental and technical benefits to, the cement industry, reducing energy costs, material consumption and waste storage areas. This study evaluates the partial replacement of blast furnace slag by BOF slag in the production of slag portland cement. Specimens were shaped with addition equivalent to 0; 1.8; 3.6 and 5.4%, in basic oxygen furnace slag weight, to the slag portland cement. The specimens were characterized by the setting time, axial compressive strength at ages 3, 7, 28 and 91 days, hot and cold expansibility. The cement with added basic oxygen furnace slag obtained gain in the initial and final strengths for all replacement levels. For the most replacement content (5.4%), the gain in compressive strength obtained amounts to 35% after 3 days and 29% after 28 days of hydration. The addition of basic oxygen furnace slag in slag portland cement composition had little influence on setting time.

Structural, 99Ru Mössbauer, dc and ac susceptibility magnetization, and magneto-transport properties of the polycrystalline Eu2Ru2O7 pyrochlore are reported in this paper. From the experimental data, we deduce that the ruthenium cations Ru4+ (S = 1) are surrounded by an unusual electronic environment, involving conduction electron polarization and extrinsic Eu3+ ions at low temperature. This situation leads to an anomalous spin-glass transition at 23 K.

Recent specific-heat data measured in Sr2YRuO6 have revealed two transition features at similar to 26 and similar to 30 K, where only one transition could be inferred before from magnetic susceptibility and transport measurements. We have investigated this temperature region using Ru-99 Mossbauer spectroscopy, magnetization, and thermodynamic measurements in order to elucidate the unusual properties in this temperature region. Below 25 K, fits to the Mossbauer spectra show that there is a unique value of the hyperfine magnetic field at each Ru site indicating static long-range magnetic order. Beyond 25 K, this static long-range magnetic order rapidly deteriorates. We have found that the temperature dependence of the Mossbauer spectra between similar to 25 and similar to 28 K can be described as due to either motional narrowing or to a temperature-dependent distribution of hyperfine magnetic fields. The Mossbauer spectra collapse to a single peak in this narrow temperature interval so that there is no evidence of static magnetic order by similar to 30 K. As a result, no evidence of the transition at 30 K is seen in the Mossbauer spectra. DOI: 10.1103/PhysRevB.87.024416

The Mossbauer spectra (MS) of powder samples of SmFe1-xCoxAsO (x = 0.0, 0.05, and 0.1) were measured in applied fields up to 9 T and at temperatures up to 298 K. SmFeAsO is magnetically ordered with T-N = 137 K and has a hyperfine magnetic field of (4.98 +/- 0.18) T at 4.2 K. In applied magnetic fields, the MS is consistent with a distribution of hyperfine magnetic fields of width H-applied + H-hyperfine. This arises because the angles between the direction of the ordered field in the crystallites making up the sample are randomly distributed about the direction of the applied field. The MS of the superconductors SmFe0.95Co0.05AsO (T-C similar or equal to 5 K) and SmFe0.9Co0.1AsO (T-C similar or equal to 17 K) are well described by a single peak from room temperature to 4.2 K indicating the absence of static magnetic order. However, the half width at half maximum, Gamma, of the peak in SmFe0.95Co0.05AsO increases with decreasing temperature from its high temperature value, 0.13 mm/s at 25 K, to 0.25 mm/s at 10 K. No such temperature dependence is seen in SmFe0.9Co0.1AsO. We analyze this temperature dependence in terms of a fluctuating hyperfine magnetic field model whose frequency at 4.2 K is found to be similar to 5-10 MHz, giving direct evidence of coexisting magnetic fluctuations and superconductivity at the interface in the phase diagram between the regions with magnetic and superconducting order. In a 5 T applied field, SmFe0.95Co0.05AsO is no longer superconducting; however, the temperature-dependent fluctuating magnetic field is still present and largely unchanged. The absence of fluctuations in superconducting SmFe0.9Co0.1AsO and their presence in superconducting SmFe0.95Co0.05AsO in zero applied field and in nonsuperconducting SmFe0.95Co0.05AsO at 5 T suggests that magnetic order is in competition with superconductivity in SmFe1-xCoxAsO.

We report new results on 119 Sn and 57 Fe Mossbauer spectra of Y1 Ba2 Cu3-z (O, N)7-x, where M is either Sn or Fe, O denotes oxygen and N denotes ni trogen, 0 ≤ X ≤ 0.5, and z = 0.05, 0.1, 0.15, 0.2. The oxygen annealed samples were superconductors, but nitrogen annealed samples were not. The Mossbauer measurements indicate four quadrupole pairs in Y Ba2 (Cu, Fe)3 O7-x, but only three pairs in Y1 Ba2 (Cu, Fe)3 N6.5. In the Sn Mossbauer spectra, the quadrupole splittings of nitrogen annealed samples are larger than that of oxygen annealed samples. In both Fe and Sn spectra, the isomer shifts of oxygen annealed samples are different from that of nitrogen annealed samples. Our study provides some information about the Cu(1) and Cu(2) sites and their surrounding environment in the Y Ba Cu system.

The Moessbauer effect (ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, B{sub hyperfine}, at the ME active site. This is the case in the ruthenates, where the temperature dependence of B{sub hyperfine} at {sup 99}Ru sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu{sub 2} and HoRu{sub 2}. Specific heat, magnetization, magnetic susceptibility, Moessbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 83.1 and 15.3 K, respectively. Despite the ferromagnetic order of the rare-earth moments in both systems, there is no evidence of a correspondingly large B{sub hyperfine} in the Moessbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out ab initio calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, asmore » a result, B{sub hyperfine} is very small at those sites. This occurs because the 4d Ru electrons form broad conduction bands rather than localized moments. These 4d conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare-earth moments.« less

Ruthenium loaded Na–Y zeolite was found to be an efficient adsorbent for achieving NOx adsorption–desorption cycles comprising adsorption under oxidizing and desorption under reducing conditions. The speciation of ruthenium was investigated using TEM, EXAFS, 99Ru Mossbauer spectroscopy and XRD in combination with Rietveld refinement. The sodium cation siting was monitored using 23Na MAS NMR. Characterization of the Ru/Na–Y adsorbent in NOx saturated and regenerated state revealed a unique cooperation of supported ruthenium nano metal particles and isolated Ru atoms in framework cavities affecting the sodium cations. Supported ruthenium nanoparticles assume a catalytic role in NO oxidation. Ruthenium atoms in framework cavities undergo switching of oxidation state during adsorption–desorption cycles. It triggers reversible sodium cation migrations from coordination with the framework in the regenerated state to coordination in sodium–water networks in supercages providing adsorption sites for NOx during adsorption. The peculiar ruthenium organization is naturally obtained upon lean–rich cycling. Ru/Na–Y adsorbent is insensitive to SOx and to the presence of CO during reductive regeneration.

Mossbauer spectra were measured from 4.2 to 145 K on a Ru-99 enriched sample of RuSr2GdCu2O8 which magnetically orders at 138 K and has a full transition to superconductivity at 8.7 K with an onset at similar to 13 K. The superconducting transition has no effect on the spectrum which is determined by the hyperfine magnetic field due to the magnetic order. At low temperatures there is a rapid decrease of this hyperfine magnetic field with increasing temperature indicating a gapless or a very low energy magnon spectrum. We use a local-moment model which includes coupling between nearest-neighbor in-plane Ru moments and between the Ru and Gd moments which are separated by a superconducting CuO layer and a SrO layer to calculate the magnon spectrum and use this to estimate the strength of the exchange interactions based on the hyperfine magnetic-field temperature dependence. The coupling strength is similar to 275 K for Ru-Ru coupling and similar to 30 K for Ru-Gd coupling.

We report new results on plasma fabricated BiSrCaCuO superconductive films and nonsuperconductive NiFeO for hybrid devices. This fabrication process takes place in an atmospheric environment and involves four steps: solution preparation, mist generation, vapor production, and cluster deposition. Among all deposition parameters, substrate temperature is the most important parameter to affect the phase formation in BiSrCaCuO films. The zero resistance temperature is 105 K for an as deposited 2223 film, and 78 g for 2212. The average crystallite size of non-superconductive NiFeO powders is approximately 35 nn, which can be utilized in hybrid devices. Mossbauer and magnetization measurement results will be given along with XRD and EDS analyses.

We report new results on nano-scaled oxide films deposited by an RF aerosol mist plasma technique: including indium tin oxide transparent conductive films; yttria stabilized zirconia, nickel iron oxide/YSZ cermet, and lanthanum strontium manganite for fuel cell applications; Bi2Sr2Ca2Cu3Ox superconductor films; gadolinium iron oxide for magnetic heat pumps; silicon oxide for protective coatings, etc. Since this deposition process occurs in an atmospheric environment, it has potential for large scale production. The maximum deposition rate is approximately 1 micrometer per minute per centimeter squared. Substrate temperatures were between 300°C and 900°C. Crystal sizes are analyzed by XRD (Shadow Programs). Some films were also characterized by resistance, optical(IR-UV-Vis transmission/reflection and FTIR) and Mössbauer measurements. Film morphology was found to be strongly dependent on deposition parameters. Controlling the deposition rate by altering solution concentration and mist feed rates, as well as altering plasma torch settings and substrate temperature allowed the formation of different film morphologies. Film density, thickness, and crystallite size could be controlled to obtain films of differing characteristics. This is advantageous to fuel cell depositions where a dense electrolyte as well as porous electrodes (anode and cathode) are required.

Nickel ferrites have been produced by the rf plasma deposition technique for the first time. This technique has promise for large scale fine particle production of ferrites. Powder x-ray diffraction linewidth measurements show an average particle size of about 55 nm. Mossbauer measurements show the presence of both the nickel ferrite and the nickel zinc ferrite with Fe3O4 created in each ferrite production process as an impurity. Magnetization and Mössbauer measurements show evidence that the aerosol prepared samples have small particle characteristics as compared to solid state reacted bulk materials.

A few atomic percent of 57Fe has been substituted for Cu in the YBa2Cu3O7−y system. Air-annealed samples are the superconducting 1-2-3 compound YBa2Cu3−x57FexO7−y while nitrogen-annealed samples are mainly the nonsuperconducting 2-1-1 compound Y2BaCu1−x57FexO5. X–ray, Meissner effect, and thermogravimetric measurements have been made on both compounds. The site dependence has been studied and compared in these two compounds by the Mössbauer effect with the result that Fe prefers the Cu(l) site in the 1-2-3 compound.

We have studied the YBa2Cu3Ox compounds using the Fe Mössbauer effect as a function of hydrogen reduction. This technique does not alter the orthorhombic crystal structure of the compound for short reduction times. On the other hand, oxygen is removed and the Tc of the sample is reduced in the process. The Mössbauer effect measurements show that oxygen leaves five-fold coordinated Cu (1) sites and creates planar oxygen coordinated sites. Mössbauer measurements in the insulating 1-2-3 phase show that there are only four and six-fold oxygen coordinations around the Cu (1) site. Some impurity phases have been created in the initial fabrication process and the Mössbauer effect shows that these impurity phases could transform to magnetic phases during the reduction process.

Hmf values are reported for Fe-57 in Ni2MnGa, and for Cd-111, Fe-57, and Sn-119 in Pd2MnSn and Ru2FeSn.