Correlation between the magnetic and electrical properties of MnSe1-x Te x chalcogenides

The coefficients of thermal expansion, lattice constant, and magnetization of anion-substituted MnSe_{1 - x}Te_x chalcogenides were measured upon cooling in zero and nonzero magnetic fields in the temperature range 4.2–600 K. Resistivity as a function of magnetic field up to 1 T was measured. The dynamic properties of the materials were studied by the ESR method. Magnetoresistance and temperature hysteresis were found in MnSe_{1 - x}Te_x solid solutions.     

Evolution of phase transitions in SrTiO3-BiFeO3 solid solutions

The dielectric and acoustic properties of (1 ? x)SrTiO₃?xBiFeO₃ solid solutions (0 ≤ x ≤ 1) have been studied in the temperature range from 4.2 to 850 K. Evolution of the antiferrodistortive transition and its suppression in the concentration range 0.1 < x < 0.2 have been revealed. X-ray diffraction data obtained at room temperature, as well as the observed acoustic anomalies combined with dielectric measurements, have been used to estimate the concentration range of the existence of the relaxor state, as well as of the formation and coexistence of the antiferromagnetic and ferroelectric phases at high BiFeO₃ concentrations.     

Raman scattering from GaSe1−xTex

The long-wavelength optical phonons of the layer GaSe_1?xTe_x have been investigated at room temperature by means of Raman scattering spectroscopy. The spectra of the Bridgman grown crystals were excited with the 1,06 μm line of the continuously operated YAG:Nd³⁺ laser. Detailed study of the Raman spectra of GaSe_1?xTe_x solid solutions showed that there is an abrupt change in the frequency-composition dependences for all observed modes. It is shown, that a phase transition from hexagonal ?-GaSe to monoclinic GaTe in GaSe_1?xTe_x solid solutions takes place in the composition range 0.27 ? × ? 0.72. Only one mode behaviour of the optical phonons was observed in GaSe_1?xTe_x system.     

Neutron diffraction studies of the magnetic properties of Pr0.5Sr0.5Co1 ? x Mn x O3 solid solutions

The crystal structure and magnetic properties of a system of Pr_0.5Sr_0.5Co_{1 ? x} Mn _x O₃ solid solutions were studied by neutron diffraction and magnetization measurements. It is shown that, at a low manganese concentration, the structure can be described by the I/2a monoclinic space group; with increasing substitution level x the structure becomes orthorhombic. For x > 0.9 the crystal structure is tetragonal at high temperatures and the symmetry is lowered to orthorhombic with lowering the temperature. The substitution of cobalt for manganese leads to the destruction of long-range ferromagnetic order near x ?? 0.25. A transition from the high-temperature ferromagnetic phase to the A-type low-temperature antiferromagnetic phase is observed at x ?? 0.93 in the temperature range 110?C160 K.     

Solid immiscibility and liquid structure in the Ga2(SexTe1−x)3 alloy system

Differential thermal analysis and X-ray diffraction studies of the system Ga₂(Se_xTe_1?x)₃ are reported and correlated with measurements of the electrical conductivity in the liquid state. The experiments reveal that Ga₂Te₃ and Ga₂Se₃ do not form a continuous series of pseudo-binary solid solutions but exhibit solid state immiscibility in the range 0.50 ? x ? 0.90. The composition dependence of the conductivity of the liquid alloys exhibits structure in the range of the solid state phase separation. Such “memory” in the liquid of a solid phase separation has not been reported previously and suggests the importance of concentration fluctuations in determining the electronic properties of the liquid alloys.     

Magnetic properties of the CoxNi1−xMnGe system

Magnetic properties of the Co_xNi_1?xMnGe system have been studied by magnetometric measurements. It was shown that the solid solutions exist for 0 ? χ ? 1, with the crystal structure of NiTiSi type. The samples with the low Co concentrations (0 ? χ ? 0.2) have antiferromagnetic properties. At higher concentrations (0.3 ? χ ? 0.5) the samples exhibit a more complex behaviour, at low temperatures having antiferromagnetic properties. At growing temperatures the change of the magnetic ordering is observed. The samples with large Co concentration (0.6 ? χ ? 1.0) are ferromagnets.     

Specific features in the behavior of the effective mass and mobility in n-(Bi, Sb)2(Te, Se, S)3 solid solutions

The thermoelectric properties of the multicomponent solid solutions Bi_2?x Sb_xTe_3?y?z Se_yS_z with substitutions of atoms in both sublattices of Bi₂Te₃ were studied. The data obtained in studies of the galvanomagnetic effects in weak magnetic fields were used to properly take into account the change in the carrier scattering mechanisms due to the substitutions Sb → Bi, Se, and S → Te in the solid solutions. The mobility μ₀ with inclusion of the degeneracy, the effective density-of-states mass m/m ₀, and the lattice thermal conductivity κ_L were calculated. An analysis was carried out for the quantities μ₀, m/m ₀, and κ_L in the solid solutions under study as functions of the composition, carrier concentration, and temperature.     

Structural phase transitions in the Bi1−x La x FeO3 system

The crystal structure and phase composition of the Bi_1?x La _x FeO₃ system have been studied by the methods of neutron and x-ray diffractions and electron microscopy. It has been revealed that a unit cell of the solid solutions at room temperature is described by the R3c, Imma, and Pnma space groups in the concentration ranges 0 < x < 0.19, 0.4 < x < 0.5, and x > 0.5, respectively. For 0.2 < x < 0.4, the solid solutions are not formed.     

Magnetic ordering in manganites substituted by chromium ions

NdMn_1?x Cr _x O₃ and Nd_0.6Ca_0.4Mn_1?x Cr _x O₃ solid solutions have been studied by neutron diffraction and magnetic measurements. NdMn_0.5Cr_0.5O₃ is found to have a magnetic structure consisting of an antiferromagnetic G-type component and a ferromagnetic component, which are caused by 3d ions. The magnetic moments of the neodymium ions are parallel to the ferromagnetic component. Nd_0.6Ca_0.4Mn_0.5Cr_0.5O₃ mainly has a G-type magnetic structure, and the magnetic moments of the neodymium ions are normal to the antiferromagnetism vector. Magnetic phase diagrams are plotted for both systems. They are interpreted on the assumption that the Mn³⁺-O-Cr³⁺ superexchange interactions are positive and the Mn⁴⁺-O-Cr³⁺ interactions are negative; the fact that manganese and chromium ions are not ordered in a crystal lattice is taken into account. Concentration magnetic phase transformations proceed through a two-phase state because of the internal chemical inhomogeneity of the solid solutions.     

Structure, transport and magnetic properties in La2xSr2−2xCo2xRu2−2xO6

The perovskite solid solutions of the type La_2xSr_2−2xCo_2xRu_2−2xO₆ with 0.25≤x≤0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for x=0.4 and 0.6. Most importantly, low field (50 Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate the presence of Co²⁺/Co³⁺ and Ru⁴⁺/Ru⁵⁺ redox couples in all compositions except x=0.5. Presence of magnetic ions like Ru⁴⁺ and Co³⁺ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization.     

Specific features of magnetoresistance during the antiferromagnet—paramagnet transition in Tm1 − x Yb x B12

The transverse magnetoresistance Δρ/ρ(H, T) of Tm_{1 ? x} Yb _x B₁₂ single crystals is studied in the ytterbium concentration range corresponding to the antiferromagnet-paramagnet transition in a magnetic field up to 80 kOe at low temperatures. A magnetic H-T phase diagram is constructed for the antiferromagnetic state of substitutional Tm_{1 ? x} Yb _x B₁₂ solid solutions with x ≤ 0.1. The contributions to the magnetoresistance in the antiferromagnetic and paramagnetic phases of the dodecaborides under study are separated. Along with negative quadratic magnetoresistance -Δρ/ρ ∝ H ₂, the magnetically ordered phase of these compounds is found to have component Δρ/ρ ∝ H that linearly changes in a magnetic field. The negative contribution to the magnetoresistance of Tm_{1 ? x} Yb _x B₁₂ is analyzed in terms of the Yosida model for a local magnetic susceptibility.     

Magnetic and dynamic properties of Sm x Mn1 − x S solid solutions

The real and imaginary parts of the magnetic permeability at frequencies of 0.1, 1.0, and 10.0 kHz, as well as the electron paramagnetic resonance (EPR) line width and g-factor, have been measured in Sm _x Mn_{1 ? x} S (0.10 < x < 0.25) solid solutions in the temperature range 5–300 K. The logarithmic dependence of the maximum in the imaginary part of the magnetic permeability on the frequency and the power-law dependence of Imμ on the temperature have been determined. The mechanism of relaxation of the magnetic moment in the magnetically ordered and paramagnetic phases has been established. The experimental results have been explained in terms of the Heisenberg model with competing exchange interactions and the formation of the antiaspiromagnetic state at low temperatures.     

Ferromagnetic-to-antiferromagnetic transition in (Hf1−xTix)Fe2 intermetallic compounds induced by geometrical frustration of the Fe(2a) sites

The ferromagnetic-to-antiferromagnetic transition in the hexagonal (Hf_1−xTi_x)Fe₂ (0?x?1) intermetallic compounds has been investigated by ⁵⁷Fe Mössbauer spectroscopy. At 10 K, the transition occurs within rather narrow concentration limits, around x=0.55–0.65. We found that the key factor governing the unexpected quick change of the magnetic structure is the magnetic frustration of the Fe(2a) sites. The magnetic frustration is caused by the noncollinearity of the Fe(6h) magnetic sublattice. The noncollinearity arises from the rotation of the magnetic moments due to the competition between the ferromagnetic exchange interactions and the antiferromagnetic Fe(6h)–Ti–Fe(6h) interaction. In the compounds with x=0.4–0.6, the temperature transitions to the antiferromagnetic state are observed. As an example, the Hf_0.4Ti_0.6Fe₂ compound is completely antiferromagnetic above 200 K.     

Crystal structure and magnetic susceptibility of (CuInSe<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(2MnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The crystal structure of samples in the (CuInSe₂)_{1 ? x} (2MnSe) _x system at room temperature and their magnetic susceptibility in the temperature range 77–1000 K are investigated. It is established that compositions with concentrations 0≤ x ≤ 0.2 form solid solutions with a tetragonal structure, space group I \(\bar 4\)2d (122). The specific magnetic susceptibility χ of samples with 0.1 ≤ x ≤ 0.4 at 77 K lies in the range 9 × 10^?4?1.6 × 10^t-3cm³/g. The temperature dependence of the inverse magnetic susceptibility of the sample with x = 0.4 suggests the presence of a component with antiferromagnetic ordering and a reliably measured Néel temperature that is characteristic of MnSe. The dependences χ = f(T) of the compositions with x = 0.1, 0.2, 0.3, and 0.4 indicate the occurrence of magnetic phase transitions with a change in the spin state.     

Structure cristallographique et magnetique de Cr1−xTixN a basse temperature

Cr_1?xTi_xN solid solutions have at room temperature a crystallographic structure of NaCl type. The space group is Fm3m. The compounds with x ? 0.15 present at low temperature an antiferromagnetic order of the fourth kind and show an orthorhombic distorsion. The space group of the deformed phase is Pnmm. The magnetic moment measured by neutron diffraction decreases with increasing titanium concentration. The compounds with x ? 0.20 do not show any magnetic order and any crystallographic distortion at very low temperature.     

An analysis of the thermoelectric efficiency of n-(Bi,Sb)2(Te,Se,S)3 solid solutions within an isotropic scattering model

A study is reported on the thermoelectric properties of n-type solid solutions Bi₂Te_3?y Se_y (y=0.12, 0.3, 0.36), Bi_2?x Sb_xTe_3?y Se_y (x=0.08, 0.12; y=0.24, 0.36), and Bi₂Te_3?z S_z (z=0.12, 0.21) as functions of carrier concentration within the 80-to 300-K range. It has been established that the highest thermoelectric efficiency Z is observed in the Bi₂Te_3?y Se_y (y=0.3) solid solution containing excess Te at optimum carrier concentrations (0.35×10¹⁹ cm^?3) and at temperatures from 80 to 250 K. The increase in Z in the Bi₂Te_3?y Se_y solid solution compared with Bi_2?x Sb_xTe_3?y Se_y and Bi₂Te_3?z S_z is accounted for by the high mobility μ₀, an increase in the effective mass m/m ₀ with decreasing temperature, the low lattice heat conductivity κ_L, and the weak anisotropy of the constant-energy surface in a model assuming isotropic carrier scattering.     

Magnetocapacitance effect in Gd<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>Mn<Subscript>1–<Emphasis Type="Italic">x</Emphasis> </Subscript>S

The capacitance and dielectric loss tangent of Gd_xMn_1–xS (x ≤ 0.2) solid solutions have been measured at a frequency of 10 kHz without magnetic field and in a magnetic field of 8 kOe in the temperature range of 90–450 K. An increase in the permittivity and a dielectric loss maximum have been detected in the low-temperature region. It has been found that the temperature of the maximum of the imaginary part of the permittivity shifts to higher temperatures with increasing concentration. The magnetocapacitance effect has been revealed for two compositions. The dielectric loss has been described in the Debye model with “freezing” dipole moments and in the orbital-charge ordering model.     

Pressure effect on magnetic properties of NdMn2−xFexGe2 (0.1⩽x⩽1.0) series of solid solutions

Temperature and pressure dependence of magnetic properties in the NdMn_2−xFe_xGe₂ series of solid solutions (0.1⩽x⩽1.0) are reported. The (P, T) magnetic phase diagrams are determined on the basis of the AC magnetic susceptibility measured in a weak magnetic field. The measurements were carried out under hydrostatic pressure up to 1.5 GPa in the temperature range 80−430 K. The reported data show that in the studied series of solid solutions, a drastic change in magnetic properties takes place in a narrow dilution parameter range (0.4⩽x⩽0.5). While taking into account the magnetic properties, the studied range of Fe content could be divided into four regions. Only in the case of x=0.3 and 0.4, the external pressure significantly influences the magnetic properties of the samples.     

EPR powder spectra of Co(II) in ZnRh2O4 spinel matrix

The EPR powder spectra of spinel solid solutions Co_xZn_1-xRh₂O₄ (x ? 0.10) have been studied in the temperature range 6–77 K. The spectra show that Co²⁺ ions occupy distorted tetrahedral sites. As the cobalt concentration increases, the spectrum of the isolated ions is gradually replaced by a strong absorption produced by antiferromagnetic exchange coupled clusters of Co²⁺ ions.     

Antiferromagnetic instability and the metal-insulator transition in Tm1 − x Yb x B12 rare earth dodecaborides

The magnetic and transport characteristics of substitutional solid solutions of the Tm_1?x Yb _x B₁₂ rare earth dodecaborides have been investigated. The measurements performed in the wide temperature range 1.8?300 K on the high-quality single-crystalline samples make it possible to conclude that as x increases, antiferromagnetic instability develops with the quantum critical point (T _N = 0) near x = 0.3 and relevant dielectrization of the electron structure in the range 0 ≤ x ≤ 0.8 takes place. With the results of the thermoelectric measurements in Tm_1?x Yb _x B₁₂, the activation energy values and their dependence on x have been determined.