Crystal structure and magnetic state of the LaMn1−x VxO3 perovskites

The crystal structure and the magnetic state of polycrystalline LaMn_1?x V_xO₃ (0.1<x<0.9) compounds have been studied by x-ray and neutron diffraction methods, as well as by magnetization and ac susceptibility measurements. It is shown that substitution of vanadium for manganese ions leaves the orthorhombic crystal structure of the compounds (space group Pnma) unchanged. The magnetic structure is observed to change from a canted antiferromagnetic ordering (wavevector k=[0, 0, 0], with the antiferromagnetic moments aligned with the a axis and the ferromagnetic component of the magnetic moment parallel to the b axis) at vanadium concentrations x<0.4 to a collinear antiferromagnetic ordering (with the magnetic moments parallel to the b axis) at x>0.8; at this transition occurs through an intermediate state exhibiting spin-glass properties.     

Electron spin resonance study of the dynamic magnetic susceptibility of CuO, Cu1−x Zn x O, and Cu1−x Li x O single crystals

Results are presented of studies of the dynamic magnetic susceptibility of CuO, Cu_1?x Zn _x O (x ≈ 1.5%), and Cu_1?x Li _x O (x ≈ 1%) single crystals. The orientational dependence of the ESR spectra was investigated at room temperature. The results for CuO are analyzed using a model of a quasi-one-dimensional antiferromagnet (S = 1/2) with anisotropic exchange interaction between Cu²⁺ spins in the chains and exchange coupling between the chains allowing for one-dimensional spin diffusion and spinon excitations. The estimated line width is of the same order of magnitude as the experimental data. Substituting Cu with Zn scarcely alters the spin dynamics of the Cu²⁺ ions, as in weakly diluted magnets. Lithium doping substantially increases the ESR line width and this is attributed to excess holes forming rapidly relaxing spin complexes with copper ions.     

Crystal structure and physical properties of magnetic shape memory alloys Ni50 − x Cu x Mn29Ga21

The phase composition, crystal structure, and physical properties (magnetization, electrical resistivity, thermoelectric power, relative elongation, and thermal expansion coefficient) of the stoichiometric alloy Ni₅₀Mn₂₅Ga₂₅ and nonstoichiometric alloys Ni_{50 ? x} Cu _x Mn₂₉Ga₂₁ (x = 0, 1, 2) with the thermoelastic martensitic transformation have been investigated. The influence of the chemical composition on the transformations and physical properties of the alloys has been determined.     

An EXAFS study of the local structure of the PbxSn1−x S solid solution

The local lead-atom environment in the Pb_xSn_1?x S solid solutions with cubic and orthorhombic structure was studied by EXAFS spectroscopy. The shortest Pb-S distance in samples with orthorhombic structure was found to be smaller by ≈0.2 Å than that in cubic-lattice samples, which is a sign of stereochemical activity of the two paired 6s ² electrons of a Pb atom. The metal atom arrangement reveals strong short-range order, which results in the formation of-Pb-Sn-Pb-Sn-... zigzag chains aligned with the c axis (in the Pbnm system) in orthorhombic samples. It was shown that the onset of such short-range order in Pb_0.5Sn_0.5S can initiate the formation of superstructures belonging to the C _2v ² or C _2v ⁷ space groups.     

Characterization and magnetic properties of electrospun Co1−x Zn x Fe2O4 nanofibers

By the electrospinning and calcination techniques, we have prepared uniform nanofibers of Co_1−x Zn _x Fe₂O₄ (0.0≤x≤0.5) ferrites with diameters of 110–130 nm. The Co_1−x Zn _x Fe₂O₄ nanofibers are single-phase spinels and the lattice constant with Zn content deviates from the Vegard’s law for these Co_1−x Zn _x Fe₂O₄ nanofibers. The Co_1−x Zn _x Fe₂O₄ nanocrystal grains by which are built nanofibers increase with calcination temperature. Variations of coercivity and saturation magnetization with calcination temperature can be explained in terms of the grain-size (D) effect. The coercivity (H _c) of Co_0.5Zn_0.5Fe₂O₄ nanofibers varies as D ^0.65 and basically follows the predicted D ^2/3 dependence based on the random anisotropy model in a D range below the single-domain size around 40 nm. The saturation magnetization of Co_1−x Zn _x Fe₂O₄ nanofibers initially increases with increasing Zn content, reaches a maximum value at x=0.3 and then decreases with further increase of Zn content, while the coercivity exhibits a continuous reduction with the increase of Zn content.     

Synthesis and magnetic properties of nanocrystalline Zn1–x Fe x O solid solutions

Bulletin of the Russian Academy of Sciences: Physics - Zn1–x Fe x O nanocrystalline solid solutions (x = 0, 0.025, 0.05) with wurtzite structure and ferromagnetic properties at room...     

Variations of phase transition temperature and enthalpy in the systems Na2Mo1− x W x O4 and Na2Mo1− y S y O4

The samples in two material systems, Na₂Mo_{1? x} W _x O₄ and Na₂Mo_{1? y} S _y O₄, were prepared by using conventional solid reactions and characterized by X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX), and difference scanning calorimetry (DSC). The XRD and EDX data indicated that all the samples in both systems were in the solid solution range. The DSC data indicated that in the system Na₂Mo_{1? x} W _x O₄, the solid–solid transition temperatures increased and in the system Na₂Mo_{1? y} S _y O₄, the solid–solid transition temperatures decreased. The total enthalpy (ΔH _total) of the solid–solid transitions in the system Na₂Mo_{1? x} W _x O₄, decreased much less than that in the system Na₂Mo_{1? y} S _y O₄. This is probably because similar to Na₂MoO₄, the solid–solid transition of Na₂WO₄ has relatively large ΔH _total, but Na₂SO₄ has much smaller solid–solid transition enthalpy. In order to modify the transition temperatures of Na₂MoO₄ and also to keep its relatively large ΔH _total, it is necessary to choose a doping material with large ΔH _total.     

Synthesis and electrochemical properties of Li8 − x Zr1 − x Nb x O6 solid solutions

New lithium-conducting solid solutions based on lithium orthozirconate have been synthesized by mutual doping of the related structures Li₈ZrO₆ and Li₇NbO₆. The main factor determining the increase in the electrical conductivity of the Li_{8 ? x} Zr_{1 ? x} Nb _x O₆ solid solutions is the formation of lithium vacancies in the tetrahedral and octahedral layers. The practical stability of the Li_{8 ? x} Zr_{1 ? x} Nb _x O₆ ceramics to metallic lithium has been studied.     

Specific features of the electronic structure and spectral properties of NdNi5 − x Cu x compounds

The spectral properties of the intermetallic compounds NdNi_{5 ? x} Cu _x (x = 0, 1, 2) have been studied using optical ellipsometry in the wavelength range 0.22–16 μm. It has been established that substitution of copper atoms for nickel leads to noticeable changes in the optical absorption spectra, plasma frequencies, and relaxation frequencies of conduction electrons. Spin-polarized calculations of the electronic structure of these compounds have been performed in the local spin density approximation allowing for strong electron correlations (LSDA + U method) in the 4f shell of the rare-earth ion. The calculated electron densities of states have been used to interpret the experimental dispersion curves of optical conductivity in the interband light absorption region.     

Magnetic and electrical properties of Mg1−x CuxO solid solutions and magnetic shielding in Cu-Mg1−x CuxO structures

Mg_1−x Cu_xO solid solutions having an NaCl structure with 0⩽x⩽0.20 are synthesized and Cu-Mg_1−x Cu_xO structures are prepared for superconductivity studies. The magnetic susceptibility χ, electron paramagnetic resonance (EPR), and electrical conductivity of the solid solutions are studied at temperatures of 5–550 K. It is shown that χ ⁻¹(T) obeys the Curie-Weiss law with a paramagnetic Curie temperature Θ close to zero and an effective magnetic moment μ _eff=1.9 μ _B, close to the 1.73 μ _B of a Cu²⁺ ion with spin S=1/2. The width ΔH of the EPR line depends weakly on temperature and increases as x is raised. The volume narrowing of the EPR linewidth ΔH is used to estimate the exchange interaction parameter, 3×10⁻⁴ eV. The g-factor is close to 2 and is temperature independent. The electrical conductivity of Mg_1−x Cu_xO at T=300 K is ≈10⁻¹¹–10⁻¹² Ω⁻¹ cm⁻¹ for x=0 and increases to 10⁻⁵–10⁻⁶ Ω⁻¹ cm⁻¹ for x=0.15–0.20. The conductivity is p-type. Magnetic shielding is observed in Cu-Mg_1−x Cu_xO structures with x=0.15 and 0.20. The possible connection of this phenomenon with interference superconductivity in the contact layer of the structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 293–296 (February 1999)     

Crystal structure and photoluminescence of (Ba1−x−ySryEux)9Sc2Si6O24

Divalent europium-doped alkaline earth metal silicate phosphors, (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (x=0.005–0.1, y=0–0.95), have been successfully prepared by solid-state reaction at 1350 °C. The analysis of X-ray diffraction shows that the compounds are in a single phase at the proper concentration of Sr²⁺. At room temperature, the Eu²⁺-activated Ba₉Sc₂Si₆O₂₄ phosphor exhibits a single emission band peaking at about 506 nm. With the increasing content of Sr²⁺, the luminescent intensity of (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ weakens, and the emission peak shifts towards red. Luminescence concentration quenching occurs when Eu²⁺ content x is more than 1 mol% in (Ba_1?x?ySr_yEu_x)₉Sc₂Si₆O₂₄ (y=0/0.2). At low temperatures (Ba_0.9?ySr_yEu_0.1)₉Sc₂Si₆O₂₄ (y=0/0.2) phosphors have two emission bands corresponding to different Eu²⁺ crystallographic sites. The high energy peak (P₁) is quenched at room temperature, while the low energy peak (P₂) weakens much more slowly owing to the energy transfer from P₁ to P₂.     

Correlation between the magnetic and electrical properties of the (VS)x(Fe2O3)2−x oxysulfide system

The correlation between the magnetic and electrical properties of the (VS)_x(Fe₂O₃)_2?x (0.9<x<1.25) oxysulfide solid solutions has been studied. The crossover of conductivity from the semimetallic to semiconducting type is accompanied by changes in the magnetic susceptibility, which are characteristic of the transition from delocalized to localized electrons. For x=1.25, a region of the ferromagnetic ordering has been established in the temperature range 90–120 K.     

Electrical,magnetic, and thermal properties of UCu5− x Pt x

We report measurements of the structural and electronic properties of UCu_{5??? x} Pt _x , a Pt-based analogue of the nFL system UCu_{5??? x} Pd _x , in the concentration range 0≤?x?≤?5. Forx?≤?2.5 and x?≥?4.5, the UCu_{5??? x} Pt _x system crystallizes in the AuBe₅ structure, but is mixed phase in the range 2.5?<?x?<?4.5. We observe a rapid suppression of long range antiferromagnetic order for small concentrations of Pt. The electrical resistivity, DC magnetic susceptibility, and specific heat of UCu_{5??? x} Pt _x in the concentration range 0.75?≤?x?≤?1 have temperature dependencies at low temperature (T?≤?10?K) consistent with the non-Fermi liquid behaviour found in UCu_{5??? x} Pd _x . Above x?=?1, there is a transition from non-Fermi liquid behaviour to Fermi liquid behaviour with no observation of any spin glass behaviour.     

Crystal structure and magnetic properties of pseudoternary TbRh2−xMxSi2(M = Ru,Ir) compounds

The structural and magnetic characteristics of the pseudoternary TbRh_2−xM_xSi₂(M = Ru, Ir) compounds were studied. The compounds crystallize in the tetragonal ThCr₂Si₂-type structure. The magnetic data were collected in the temperature range 70–300 K. Their magnetic susceptibilities satisfy the Curie-Weiss law in the temperatures higher than 130 K. The magnetic moment of the rare earth atom is larger than of the free Tb³⁺ ion. A modified RKKY theory with included interaction between the conduction electrons was applied to explain the variation of properties of the compounds.     

Specific features of electronic and magnetic states of the Y3Co binary compound in the (Gd1 − x Y x )3Co solid solution system

The electronic and magnetic properties of Y₃Co single crystals have been studied using neutron diffraction and electrical measurements. It has been established that these properties of Y₃Co and (Gd_{1 ? x} Y _x )₃Co crystals differ substantially. The most probable models of modification of the physical properties of the binary compound have been discussed.     

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.     

Magnetic properties of (Mn1 − x Fe x )1.68Sn solid solutions

Solid solutions in the (Mn_{1 ? x} Fe _x )_1.68Sn system (x ≤ 0.5) with a Ni₂In-type structure are synthesized by the solid-phase reaction method in a stepwise temperature regime. The unit cell parameters a and c decrease with an increase in the iron concentration in the alloys and become equal to a = 0.430 nm and c = 0.538 nm for the (Mn_0.5Fe_0.5)_1.68Sn alloy. A superstructure with the unit cell parameters a _ss = 3a and c _ss = c is revealed in alloys of the system under investigation. The specific magnetization of the alloys increases nonlinearly from 53 G cm³ g^?1 in the Mn_1.68Sn alloy to 72 G cm³ g^?1 in the (Mn_0.5Fe_0.5)_1.68Sn solid solution. The Curie temperature changes from 270 K in the initial alloy of the composition Mn_1.68Sn to 365 K in the alloy of the composition (Mn_0.5Fe_0.5)_1.68Sn. All solid solutions in the (Mn_{1 ? x} Fe _x )_1.68Sn (x ≤ 0.5) system exhibit metallic conductivity in the temperature range from 77 to 450 K.