NMR and magnetization study of the mixed systems (Pd1-xCux)2 MnIn and (Pd1-xNix)2 MnIn

Systematic NMR and magnetization data with concentration show that for decreasing x these systems go from ferromagnetic (F) to anti-ferromagnetic (AF) order by passing a mixed phase region where both magnetic orders coexist in different domains. The magnetic phase diagrams for both alloy series are nearly coincident. The NMR spectra show that the Cu or Ni atoms substitute randomly onto Pd sites and we find no evidence that the participation of Mn atoms in F or AF domains is at all correlated with their nearest neighbour environments. In the limit where the AF order becomes largely dominant the samples exhibit a magnetic anisotropy after field cooling.     

Magnetization reorientation in HoCo5-xNix and HoCo5-xCux compounds

The studies of magnetic anisotropy of HoCo_5-xNi_x and HoCo_5-xCu_x compounds in the temperature range between 60 and 293 K are presented. The magnetization reorientation from the c-axis to the base plane has been observed. The experimental results are analyzed on the base of the Irchin and Rozenfeld model.     

Spin-glass-like phase behaviour in CeNi2−xCuxSn2

We report the results of our investigation in CeNi_2−xCu_xSn₂ (x=0, 0.4, 1.0, 1.6 and 2.0), a new pseudoternary series with CaBe₂Ge₂-type tetragonal structure. Substitution of Cu for Ni leads to a linear increase in the constants a, c and the unit cell volume v. As probed by the low temperature dependence of ac susceptibility χ_ac(T), the T_f temperature, which corresponds to the freezing temperature of the spin-glass clusters, is annihilated above 2.0 K significantly for the samples with x≥1.6. This observation proves conclusively that the Ni-rich samples in the series CeNi_2−xCu_xSn₂ have the advantage of forming the spin-glass-like state.     

Conductivite ionique des systemes Kx(Znx/2Ge1-x/2)O2 et Kx(GaxGe1-x)O2 de structure cristobalite

The crystal chemistry of the K_x(Zn_x/2Ge_{1-$\text{x}\text{2}$})O₂ and K_x(Ga_xGe_1-x)O₂ systems has been investigated. In each of them a solid solution with a cristobalite-type structure has been obtained with a 0.90?×?1 range. The K⁺ conductivity increases strongly with vacancy content, while the activation energy remains nearly constant.Influence of various crystal chemical parameters on the conductivity (lattice covalency, size of the bottlenecks, etc...) is discussed.     

Study of polycrystalline bulk CuIn1-xGaxTe2

Polycrystalline CuIn_1−xGa_xTe₂ bulk films were synthesized by reacting, in stoichiometric proportions, high purity Cu, In, Ga and Te in a vacuum sealed quartz ampoule. The phase structure and composition of the bulk films were analysed by X-ray diffraction and energy-dispersive X-ray analysis, respectively. The bulk samples, of p-type conductivity, are found to be near-stoichiometric, polycrystalline, with tetragonal chalcopyrite structure, predominantly oriented along a direction perpendicular to the (1 1 2) plane. Photoluminescence spectra were recorded at 7 K and 700 mW to characterize the defects and the structural quality. The main peak as a function of composition has been studied.     

Structural and Magnetic Properties of NiFe2−2xSnxCuxO4

The substituted nickel ferrite (NiFe_2−2xSn_xCu_xO₄, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe³⁺ ions by Sn⁴⁺ and Cu²⁺ cations on the structural and magnetic properties of the ferrite was studied by means of ⁵⁷Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe₂O₄ adopts a fully inverse spinel structure of the type (Fe)[NiFe]O₄, Sn⁴⁺ and Cu²⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe_1−2xSn_xCu_x]O₄, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe_2−2xSn_xCu_xO₄ samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement.     

Magnetic properties of the Ce1-xLaxMn2Si2 system

Magnetic properties of the Ce_1-xLa_xMn₂Si₂ system were investigated by means of neutron diffraction and magnetometry. The samples with low La concentration (x?0.5) have antiferromagnetic properties. A transition from an antiferromagnetic to a ferromagnetic state can be observed for x=0.6 (for increasing temperature). More La leads to the samples being ferromagnetic. A collinear magnetic structure is seen from the neutron diffraction spectra. From all the results known up to now it follows, that type of magnetic ordering, i.e. antiferro- or ferro-depends on the Mn-Mn interatomic distances in the basal plane.     

Magneto volume effects in TiBe2

From magnetostriction results on TiBe₂ and copper doped TiBe₂, we estimate magneto volume interactions. We deduce that the lattice expansion is not a decisive factor for the transition to ferromagnetism in the copper doped series.     

Magnetic properties of system HgxZn1-xCr2Se4

Magnetic moments, magnetic susceptibilities and optical absorption of the system Hg_xZn_1-xCr₂Se₄ have been measured. A correlation is found between the optical and the magnetic properties.     

Reflectivity of Sn(Se1-xSx)2 mixed crystals

Reflectivity measurements in fundamental absorption range (3.6–13 eV) have been made on Sn(Se_1-xS_x)₂ mixed compounds for several compositions (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0). The composition dependence of the energy location of the reflectivity structures is found to be non-linear and different according to the electronic transitions involved. This behaviour is discussed in terms of electronic structure evolution related to the anion substitution.     

Thermo-optical response of VxTi1-xSe2 in the plasmon reion

It is shown that some structure growing on the high energy side of the plasmon when cooling TiSe₂ crystals through the transition temperature is smeared out with vanadium concentrations of the order of 1% and that the plasmon lifetime is considerably affected both by temperature and vanadium content.     

Infrared and structural studies of Mg1-xZnxFe2O4 ferrites

Compositions of polycrystalline Mg-Zn mixed ferrites with the general formula Mg_1−xZn_xFe₂O₄ (0≤x≤1) were prepared by the standard double sintering ceramic method. The structural properties of these ferrites have been investigated using X-ray diffraction and infrared absorption spectroscopy. The lattice parameter, particle size, bonds length, force constants, density, porosity, shrinkage and cation distribution of these samples have been estimated and compared with those predicted theoretically. Most of these values were found to increase with increasing Zn content. The energy dispersive (EDS) analysis confirmed the proposed sample composition. The scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs showed aggregates of stacked crystallites of about 200-800 nm in diameter. Far infrared absorption spectra showed two significant absorption bands. The wave number of the first band, ν₁, decreases with increasing Zn content, while the band, ν₂ shifts linearly towards higher wave numbers with Zn contents, over the whole composition range. The room temperature electrical resistivity was found to decrease as Zn-content increases. Values of the vacancy model parameters showed that the packing factors P_a and P_b decrease, the fulfillment coefficient, α, remains almost constant and the vacancy parameter, β, strongly increases with increasing Zn content in the sample. The small values of P_a, P_b, α and the strong increase of the vacancy parameter, β, indicate the presence of cation or anion vacancies and the partial participation of the Zn²⁺ vacancies in the improvement of the electrical conductivity in the Mg-Zn ferrites.     

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.     

Low temperature specific heat and magnetization of (Fe1-xTx)Be2

Low temperature specific heat and magnetization results on (Fe_1-xT_x)Be₂ with T= V, Cr, Mn, Co and Ni are presented. The interpretation of these results is based on the virtual bound states concept.     

Investigations of Sm6(Mn1-xFex)23 system

The new Sm₆(Mn_1-xFe_x)₂₃(0?x?1.0) system hasbeen synthesized and investigated in a wide temperature range by the X-ray, magnetometric and Mössbauer effect methods. The X-ray studies show that the system forms solid solutions which are isostructural with the Th₆Mn₂₃ type crystal structure throughout the entire compositional range. Both Fe-rich and Mn-rich regions of the system are magnetically ordered and are separated from each other by the non-magnetically ordered 0.22?x?0.33 region. The substitution of Fe atoms for Mn atoms in the Mn-rivh region and similarly of Mn atoms for Fe atoms in the Fe-rich region decreases both the Curie temperature and the value of the magnetic moment per molecule. The temperature dependence of the reciprocal susceptibility obeys the Néel law. The Mössbauer absorption spectra reflect wide distributions of the ⁵⁷Fe hyperfine interaction parameters, and disappearance of long range magnetic coupling of Fe atoms in the magnetically ordered x=0 to 0.22 composition range.     

Structure and magnetic order of Cr-rich Rb2Cr1-xMnxCl4 crystals

The distorted K₂NiF₄-structure and the magnetic behaviour of the quasi two-dimensional magnetic system Rb₂Cr_1-xMn_xCl₄ (0 ? x ? 0.5) are studied by neutron diffraction and magnetic measurements. Strong correlations between ferromagnetic coupling and cooperative Jahn—Teller order are indicated by their occurence in the same concentration range 0 ? x ? 0.41.The percolation threshold x_F near x = 0.41 and the x, T-dependence of the para- to ferro-magnetic phase boundary are quite similar to that found in systems with non-magnetic impurities. Further we report the magnetic moment magnitudes in this percolative system.     

On the magnetic properties of Y(FexCo1-x)2 compounds

The composition dependence of the mean magnetic moment of cobalt atoms in Y(Fe_xCo_1-x)₂ compounds is analysed in the local environment model. Cobalt has a magnetic moment of 1.56 μ_B if there are at least two Fe atoms as nearest neighbours. The maximum in the composition dependence of the transition metal moments is due to the magnetic contributions of iron atoms only. The thermal variation of reciprocal susceptibility obeys a Curie-Weiss behaviour, in addition to the Pauli paramagnetic term. Finally, the influence of the variable magnetic interactions on the transition metal moments is discussed.     

Synthesis and characterization of apatite-type La9.67Si6-xAlxO26.5-x/2 electrolyte materials and compatible cathode materials

Apatite silicates have recently been reported as promising electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, a series of apatite-type compounds La_9.67Si_6-xAl_xO_26.5-x/2 (LSAO) with x = 0-2 are synthesized by the sol-gel process at calcining temperature of 800-900 °C. Thermal expansion coefficient, relative density and electrical conductivity of these samples with different Al doped contents are investigated. A symmetrical cell, which is composed of La_9.67Si₅AlO₂₆ electrolyte and (La_0.74Bi_0.10Sr_0.16)MnO_3+δ (LBSM) cathode, is fabricated and electrochemically characterized. LBSM cathode shows a good electrochemical performance, which proves LBSM to be a promising candidate cathode for LSAO-based electrolyte.     

Magnetic ordering in the random mixture CsMn1-xCoxCl3·2H2O

Previous neutron measurements in the mixed magnetic system, CsMn_1-xCo_xCl₃·2H₂O have been extended to samples with x = 0.035, 0.05 and 0.075. In this system two kinds of magnetic ions with competing orthogonal spin anisotropies are randomly distributed. The ordering temperatures T_N (x are clearly detected through the appearance of magnetic Bragg reflections. However, there are no indications for the existence of any other phase transition under the experimental conditions. The observed magnetic phase below T_N (x) corresponds to an oblique antiferromagnetic phase predicted for such a system.     

Spin-glass-like behaviour of the mixed spinel systems MnxZn1-xCr2O4 and Mn0.75Mg0.25(Cr1-yVy)2O4

NMR and susceptibility measurements have been made on a randomly mixed insulating ferrimagnet and antiferromagnet, Mn_xZn_1-xCr₂O₄. The thermoremanence and the induced unidirectional anisotropy were observed for concentrations lower than x = 0.80, after field cooling. The compound Mn_0.75Mg_0.25Cr₂O₄ shows similar behaviour. When the latter is doped with V³⁺ at the B sites, its magnetic anisotropy increases strongly, but the change in the unidirectional anisotropy is smooth.