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.     

Resistance measurements at high pressure in the system BaPb1-xBixO3

Resistance measurements have been made in the system BaPb_1-xBi_xO₃ at pressures of up to ～ 125 kbar at room temperature. A distinct change in slope of R/R₀ vs P indicates the onset of a transition, possibly to the metallic state, which takes place continuously over a wide range of pressure.     

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.     

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.     

Exciton and impurity electroabsorption in GaSexTe1-x〈Sn〉 single crystals

The exciton and impurity electroabsorption has been studied in GaSe_xTe_1-x〈Sn〉 (0.7 ?χ?1) exhibiting the properties of residual conductivity (RC). It has been shown that the broadening of the negative exciton peak, the nature of the field dependence of the electroabsorption signal, and its anisotropy in the exciton and impurity region are associated with the presence of internal chaotic fields E_int ≈ 10³ ? 10⁴ V cm^?1 coming into play because of the fluctuating distribution of the tin impurity and the defects inherent in layer crystals. Based on investigations of the impurity electroabsorption (IEA), the depth of occurence (hv = 1.18 eV) and the concentration (N = 10¹⁶cm³) of impurity centres have been determined.     

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.     

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.     

Concentration dependence of the Ce3+ and Tb3+ luminescence of Ce1-xTbxMgAl11O19

The quenching of the Ce³⁺ emission and the increase of the Tb³⁺ emission with increasing x of Ce_1-xTb_xMgAl₁₁O₁₉ for x ? 0.35 is ascribed to energy transfer from Ce³⁺ to Tb³⁺, which is restricted to nearest rare earth neighbours. This transfer is almost complete at x ? 0.35. The decrease of the Tb³⁺ emission at higher Tb³⁺ concentrations is not due to Tb³⁺ concentrational quenching, but due to the limited solubility of Tb³⁺ in the CeMgAl₁₁O₁₉ phase.     

Effect of Ni doping on structural and magnetic properties of Co1-xNixFe1.9Mn0.1O4

Nickel-substituted iron-deficient cobalt ferrite containing small quantity of manganese having the chemical composition Co_1−xNi_xFe_1.9Mn_0.1O₄ with x=0.2, 0.4, 0.6 and 0.8, were prepared by the standard double sintering ceramic technique. The thermal decomposition process of the powder (i.e. grounded starting materials) was studied by thermo-gravimetric analysis (TGA). The compositional analysis was carried out by EDAX pattern. The infrared spectroscopy studies show the presence of tetrahedral and octahedral group complexes within the spinel phase. Microstructural features were studied by scanning electron microscopy, grain size found to be decreasing with increasing Ni content. Room temperature hysteresis measurement was carried out under the field of 6 kOe for all samples which reveal monotonic decrease of magnetization at 6 kOe (M_6 kOe). The coercive field (H_c) decreases up to concentration of Ni²⁺ (x=0.6) and a small increase was observed for x=0.8. Initial permeability (μ_i) plotted against temperature at 10 kHz shown sharp drop at Curie temperature and values observed at transition are found to be dependent on the nickel content.     

Observation of disappearance of cooperative Jahn-teller distortion in the two-dimensional magnetic system K2CuxZn1-xF4 by Raman scattering experiments

Raman spectra in the two-dimensionla diluted system K₂Cu_xZn1-xF4 are reported. The problem how the cooperative Jahn-Teller distortion (whose existence in the c-plane is well confirmed for K₂CuF₄) is destroyed with decreasing x is discussed on the basis of observed behaviours of Strokes lines for some characteristic vibrational modes in spectra.     

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 studies of the alloy system GdInxAg1-x

The structural and magnetic studies below room temperature of the alloy system GdIn_xAg_1-x(0?x?1) are reported. It has been found that alloys with x?0.5 crystallize in CsCl type cubic structure, but the distortion of the unit cell starts for alloys with x#62;0.5 and for these alloys the unit cell becomes tetragonal. No phase change is evident from the low temperature (295-8 K) structural studies. However, a break appears in the X^-1_m vs. T linear plot of each alloy of this system at a specific temperature (designated as break temperature T_B). The variation of T_B with x is similar to the variation of phase transition temperature with x reported for LaIn_xAg_1-x. Close agreement has been found in the values of effective magneton number (p), magnetic ordering [Néel (T_N) or Curie (T_C)] and paramagnetic Curie (θ_p) temperature for materials studied by us and earlier workers. The variation of magnetization with applied field strength (2.5-65)×10⁵ Am^-1) at 4.2 K has also been reported for ferromagnetic of this system. It has been concluded that alloys with 0.4?x?0.6 are simple ferromagnets with parallel alignment of magnetic moment in the ground state. The angular arrangement of the magnetic moment starts appearing in the ground state for alloys with x?0.4 for x#62;0.6 and continues till x becomes closure to 0.17 or 0.84. The alloys with x=0.17 or x=0.84 have θ_p and T_C equal to zero and appear paramagnetic. Angular arrangement in spins again appear for alloys with x?0.17 or x#62;0.84, however all materials with 0?x?0.17 or 0.84?x?1 remain antiferromagnetic.     

The properties of acicular particles of (γ-Fe2O3)x(Fe3O4)1-x

It is known that acicular particles, initially of Fe₃O₄, which have been partially oxidised, show anomalous properties e.g. in the variation of H_c with composition. It is shown that these can be explained by considering the particles to comprise an inner core of Fe₃O₄ with an outer layer of γ-Fe₂O₃. Owing to the large change in volume which occurs on oxidation, these mutually stress each other. Over a certain range of composition, the stress field interacts with the magnetization to increase H_c, and it is also responsible for H_c increasing with time after the oxidation process. A similar situation applies to partially reduced γ-Fe₂O₃.     

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.     

Magnetic properties of ErxY1−xF3 solid solutions

The Er_xY_1−xF₃ (x=0.1, 0.2, 0.7, 0.9, 1) solid solutions were synthesized and characterized by X-ray powder diffraction and magnetic measurements. The crystal structure refinements done by the Rietveld profile method show that no significant change of the structure parameters with the erbium concentration occurs. On the basis of DC susceptibility measurements in the 2-300 K range the lowest four crystal field levels have been determined, giving the ground level magnetic moment value of 6.7 μ_B. Results of M(H) studies point to the presence of complex exchange interactions between erbium ions.     

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.     

Raman scattering from GaSxSe1-x

The non resonant Raman scattering spectra of GaSe, GaS and of eight different mixed crystals GaS_xSe_1-x are presented. The frequencies of some vibrational modes shift continuosly from GaSe to GaS indicating that the mixed crystals are homogeneous. The discontinuous shift of some other modes is explained either by the change of the stacking of the layers, or by a ‘two mode’ behaviour as previously observed in other types of mixed crystals. Moreover, local vibrational modes are observed.     

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.     

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.     

Dielectric anomaly in amorphous Si100-xAux system

In amorphous Si_100-xAu_x system the dielectric constant is decreasing with increasing frequency or with decreasing temperature at $\text{x ? 5.5\%}$. This is explained by considering the dispersion of the variable range hopping contribution to the dielectric constant. The dielectric constant at sufficiently high frequency or at sufficiently low temperature is increasing rapidly with increasing x in the region x ? 5.5%, which predicts the occurrence of the nonmetal-metal transition.