Optical absorption and thermoluminescence studies on LiF-Sb2O3-B2O3 glasses doped with Ni ions

20LiF-(30−x)Sb₂O₃-50B₂O₃:xNiO glasses with the value of x (ranging from 0 to 1.0 mol% in steps of 0.2) were prepared. A number of studies, viz. differential scanning calorimetry, optical absorption, magnetic susceptibility and thermoluminescence, on these glasses were carried out as a function of nickel ion concentration. An anomaly has been observed in all the properties of these glasses when NiO concentration is about 0.6 mol%. The results of these studies were analysed in the light of different environments of nickel ions in the glass network.     

Magnetic properties of xCoO.(1−x)[2B2O3.PbO] glasses

The results of magnetic studies on xCoO.(1?x)[2B₂O₃.PbO] glasses with 0?x?50 mol.%, are reported. These results show evidence that the cobalt ions, in this glass system, are in bivalent state and magnetically isolated, having magnetic moments μ=(4.50±0.06)μ_B.     

Magnetic properties of xCuO · (1 - x) [2B2O3 · PbO] glasses

The results of magnetic studies on xCuO · (1 ? x) [2B₂O₃ · PbO] glasses with 0 ? x ? 50 mol.%, are reported. These results evidenced that the copper ions, in this glass system, are in Cu²⁺ and Cu⁺ valence states. From Curie constant is determined the amount of the copper ions in bivalent state. For glasses with x > 5 mol.% CuO, an antiferromagnetic behaviour is evidenced.     

Magnetic properties of (Ti1-xVx2O3 powders

The magnetic susceptibility of (Ti_1-xV_x2O₃ powders with 0 ? x ? 0.12 has been measured over the temperature range 4.2–300 K. The data show a Curie-Weiss behaviour between 20 and 150 K. As x is increased, the effective magnetic moment per V atom first decreases from 3.8 to 1.8 μ_B shows a steep increase for x = 0.02 and reaches a limit of 1.8 μ_B. These results are discussed in connection with a theoretical model proposed by Van Zandt, involving a narrow V impurity band.     

EPR and magnetic susceptibility studies of the interaction between Cu2+ and Mn2+ ions in x(CuO·MnO)(1−x)[2B2O3·K2O] glasses

EPR and magnetic susceptibility experiments have been performed on x(CuO·MnO)(1?x)[2B₂O₃·K₂O] glasses with x varying in the range 0?x?50 mol.%. For x?3 mol.% both Cu²⁺ and Mn²⁺ ions are present mostly as the isolated species. The increase of the g-tensor values and bonding parameters (α², β², δ²) for Cu²⁺ ions together with the increase of TM ions concentration in the 0.2–1 mol.% range was noticed. In the case of 5 ? x ? 30 mol.% the dipole-dipole and superexchange interactions occur between transition metal ions, the first type of interactions prevailing in this range of concentration. For x30 mol.% the superexchange interaction prevail. The strong interaction between Cu²⁺ and Mn²⁺ gives rise to the exchange coupled Cu²⁺Mn²⁺ pairs in the studied glasses with x 3 mol.%.     

Chemical order and magnetic properties of the Ni2−xMnSb system

The results of extensive magnetisation, X-ray and neutron powder diffraction measurements on the intermetallic compound series Ni_2-xMnSb, for 0?x?1, are reported. For x ?0.4, a high degree in the C1_b structure is observed, but for x?0.3, some disorder is evident. The series is ferromagnetic, with Curie temperatures rising from 368 to 732 K with decreasing nickel concentration. The magnetic moments all lie in the range (4.0±0.3)μ_B, with a maximum at a composition near x=0.45. The magnetic moments are largely associated with the ordered manganese sites, but it is possible that a small negative moment ?0.25μ_B may be associated with the “nickel sites” for x?0.3. This latter moment may be accounted for by disordered Mn atoms antiferromagnetically aligned.     

Magnetic and magneto-transport properties of double perovskite Ba2−xSrxFeMoO6 system

The structural magnetic and magneto-transport properties of double perovskite system Ba_2−xSr_xFeMoO₆ (0?x?1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe-Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba₂FeMoO₆ exhibits saturation magnetic moment value of 3.54 μ_B/f.u. at 85 K in a magnetic field of 6000 Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73 μ_B/f.u. and MR value of 7.08% (1 T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail.     

EPR and magnetic susceptibility studies of xCuO·(1−x)[2B2O3·Li2O] glasses

The results of EPR and magnetic susceptibility studies on xCuO·(1?x)? [2B₂O₃·Li₂O] glasses with $\text{0?x?30 mol \%}$, are reported. The modification of EPR spectra with the increasing of CuO content are explained supposing that these are the result of the superposition of two EPR signals, one showing the hyperfine structure typical for isolated Cu²⁺ ions and other consisting from a broad line centered at g ～ 2 typical for the clustered Cu²⁺ ions. The values of the EPR parameters prove that the coordination of isolated Cu²⁺ -complexes remains approximately the same and show that Cu²⁺ ions are situated in axially distorted octahedral vicinities. EPR measurements have shown that the Cu²⁺ ions are present mostly as the isolated species when $\text{x?5 mol \%}$. Beside the dipole-dipole coupling between Cu²⁺ ions, the magnetic measurements suggest that for x>10 mol % superexchange interactions appear, too. From Curie constant is established that in this glass system the copper ions are in Cu²⁺ and Cu⁺ valence states. Also, the amounts of the copper ions in bivalent state are determined.     

Nickel ion—A structural probe in BaO-Al2O3-P2O5 glass system by means of dielectric, spectroscopic and magnetic studies

BaO-Al₂O₃-P₂O₅ glasses containing different concentrations of NiO (ranging from 0 to 1.0 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption spectra), magnetic susceptibility and dielectric properties (constant ε′, loss tan δ, AC conductivity σ_AC over a range of frequency and temperature) of these glasses have been carried out. The studies on chemical durability indicate that there is a significant increase in the corrosion resistance of the glasses; where as the results of differential thermal analysis suggests that there is a substantial improvement in the glass forming ability, with increase in the concentration of NiO up to 0.6 mol% in the glass matrix. The optical absorption, magnetic susceptibility and IR spectral studies point out nickel ions occupy both tetrahedral and octahedral positions in the glass network; the later positions seems to be dominant when the concentration of NiO is beyond 0.6 mol% in the glass matrix. The studies of dielectric properties reveal that the presence of nickel oxide in the glass network causes a considerable improvement in the insulating strength of the se glasses when the concentration of NiO?0.6 mol%.     

Stoner excitations in the strong itinerant amorphous ferromagnets FexNi80−xB18Si2 and Fe80B20

Accurate measurements of the static magnetization of the amorphous ferromagnets Fe_xNi_80?xB₁₈Si₂ (x = 15, 20, 40, 60%) and Fe₈₀B₂₀ are reported. The results are analyzed in terms of spin-wave and Stoner excitations, and the latter indicate strong itinerant ferromagnetism with a Stoner gap Δ varying between 20 and 60 K. The other fitting parameters give values of the spin-wave stiffness and a quantity simply related to the saturation magnetization. The well-known anomaly regarding the spin-wave stiffness observed in earlier measurements in thus explained quantitatively.     

Effect of quenching wheel speed on the structure, magnetic properties and magnetoimpedance effect in Co64Fe4Ni2B19−xSi8Cr3Alx (x=0, 1 and 2) melt-spun ribbons

Melt-spun ribbons of Co₆₄Fe₄Ni₂B_19−xSi₈Cr₃Al_x (x=0, 1 and 2) alloy at wheel speed of 25 m/s and Co₆₄Fe₄Ni₂B_19−xSi₈Cr₃Al₁ alloy at different wheel speeds (25, 30, 35 and 40 m/s) have been prepared and investigated for structural and magnetic properties and magnetoimpedance effect. Based on the results obtained, it was shown that replacement of B by Al can improve the magnetoimpedance ratio (MIR) and the highest value of MIR (191%) was observed for the sample with X_Al=1 at wheel speed of 25 m/s. Further, it was seen that the higher quenching wheel speed gives rise to a higher coercivity and lower magnetic permeability/MIR value.     

Magnetic phase diagrams of Ho1−xDyxNi2B2C

We performed the magnetization measurement on Ho_1−xDy_xNi₂B₂C single crystals (x=0.1, 0.2, 0.3, 0.4, and 0.6) with magnetic field applied perpendicular and parallel to the c-axis. But only for the magnetic field perpendicular to the c-axis, the increase of Dy³⁺ concentration affects the magnetically ordered states of HoNi₂B₂C compound and makes the phase diagram more complicated. The antiferromagnetic ordering state attributed to Dy³⁺ sublattice starts to appear from a case of x=0.2 and finally the magnetic phase diagram becomes analogous to that of DyNi₂B₂C as x is increased which is consistent with the neutron scattering result.     

L'etude cristallographique et par effet mössbauer des solutions solides V2O5Fe2O3

Using the Mössbauer effect, we analyse the behaviour of (V₂O₅)_1?x(Fe₂O₃)_x solid solutions with the starting composition x = 1?15 mol.% Fe₂O₃. The number of iron ions dissolved in V₂O₅ lattice depends on the initial composition x of Fe₂O₃ and tends to a maximum value corresponding to 4 mol.% Fe₂O₃. The composition dependence of the quadrupole splitting and isomer shifts is presented.     

Magnetic properties of CuInSe2-(FeSe)2 solid solutions

Measurements of the magnetic characteristics of Cu_{1 ? x} In_{1 ? x} Fe_2x Se₂ solid solutions and their approximation by Langevin and Curie equations show that the properties observed in samples are the result of antiferromagnetic clusters in which magnetic moments fall to ～0.8 μ_B/atom as x rises, confirming that the antiferromagnetic interaction in the samples grows stronger.     

On the iron valence states in B2O3-PbO-GeO2 glasses

The Mössbauer effect measurements performed on 20Fe₂O₃ 80 3B₂O₃ (1?x)PbO xGeO₂ glasses show that the ratio between the number of ferrous ions to the total number of iron ions decreases by increasing the GeO₂ content. The Curie constants calculated from the distribution of iron cations obtained by Mössbauer effect data are in agreement with the values determined from magnetic measurements. Finally, we discuss the influence of the glass composition and melting temperature on the iron valence states.     

Magnetic properties of the Ce2Fe17−xMnx helical magnets up to high magnetic fields

Magnetic properties of the Ce₂Fe_17−xMn_x, x=0–2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1<x?2 are helical ferromagnets or helical antiferromagnets at low and high T, respectively. Mn ions in the system carry average magnetic moment of 3.0±0.2 μ_B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce₂Fe_17−xMn_x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce₂Fe_17−xMn_x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce₂Fe_17−xMn_x, x=0.5–2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated.     

Magnetic properties of Ni0.8Cu0.2−xGex solid solutions

The results of magnetic measurements performed on Ni_0.8Cu_0.2-xGe_x solid solutions, with x ? 0.10 are reported. The saturation magnetization, Curie temperature and effective nickel moments decrease nearly linear when substituting Cu by Ge. The ferromagnetic resonance measurements show that the g values are not dependent on composition. Finally, the magnetic behaviour of nickel in these solid solutions is analysed.     

Magnetic order in palladium-based Heusler alloys Part I: Pd2MnIn1−xSnx and Pd2MnSn1−xSbx

Magnetization, susceptibility, X-ray and neutron diffraction measurements have been made on the two series of alloys Pd₂MnIn_1?xSn_x and Pd₂MnSn_1?xSb_x, for 0 ? x ? 1. All were single phase and were chemically ordered intermetallic compounds with the Heusler L2₁ structure in which the Mn atoms occupy an f.c.c. sub-lattice. At all compositions the alloys were magnetically ordered with a moment of ～4.3 μ_B located at the Mn sites. At the In-rich end the magnetic order is antiferromagnetic f.c.c. type 2. As Sn is increasingly substituted for In there is a change in magnetic order first to antiferromagnetic f.c.c. type 3A and then to ferromagnetism. All the alloys in the Sn/Sb series are ferromagnetic and in both series there is an increase in the ferromagnetic exchange interactions with increasing electron concentration.     

The valence states of manganese ion in potassium-borate oxide glasses

EPR and magnetic susceptibility measurements have been performed on xMnO·(1-x) [2B₂O₃·K₂O] with 0?x?50 mol %. The X-ray diffraction analysis showed that in this glass system homogeneous glasses are formed up to x = 70 mol %.EPR and magnetic susceptibility data have shown that in the glasses with x ? 5 mol % only Mn²⁺ ions are present as magnetically isolated species. EPR spectra are modified with the increasing of manganese ions content. In the concentration range 0.5 ? x ? 5 mol %, the spectra are characterized by appearance of three resonance absorptions at g ? 4.3 and g ? 3.3 without hyperfine structure, and at g ? 2.0 with hyperfine structure. For the glasses with x >62; 5 mol %, the resonance spectra are characterized by the appearance of the broad line at g ? 2, characteristic for clustered ions. The magnetic susceptibility data suggest the appearance of superexchange interactions for x >62; 5 mol %. From Curie constant values and qualitative chemical analysis we have established that in the glasses with x ? 10 mol % both, Mn²⁺ and Mn³⁺ ions are present.     

Reactivity and XAFS study on (1−x)CeO2-xNiO (x=0.025-0.3) system in the two-step water-splitting reaction for solar H2 production

The redox reaction of Ce⁴⁺-Ce³⁺ promoted by the catalytic function of nickel ions in a (1−x)CeO₂-xNiO solid solution was investigated for solar H₂ production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O₂-releasing reaction with (1−x)CeO₂-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H₂ gas evolved by the reduced form were 1.2-2.5 cm³/g and the evolved gases amounts ratio of H₂/O₂ was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H₂O=H₂+1/2O₂). The maximum amounts of evolved H₂ and O₂ gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO₂-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O₂-releasing and H₂-generation reactions with (1−x)CeO₂-xNiO solid solution were repeatable with the redox system of Ce⁴⁺-Ce³⁺, which was enhanced by the catalytic function of Ni²⁺-Ni⁰.