Growth,structure, and magnetic properties of CuFeTe<Subscript>2</Subscript> single crystals

CuFeTe₂ single crystals were grown and the temperature dependence of their magnetic susceptibility in the temperature range 1.8–400 K was investigated. It is found that the magnetic susceptibility shows anomalies at temperatures T _s = 65 and T _N = 125 K. At T > 125 K, the crystal is in the paramagnetic state controlled by Fe²⁺ and Cu²⁺ ions with an effective magnetic moment of 1.44 μB.     

Growth and characterization of Fe1 ? x M x VO4 single crystals (M = Al, Cr, Co, Ga)

Triclinic Fe_{1 ? x} M _x VO₄ single crystals (M = Al, Ga, Co, Cr) have been grown by the flux method from systems based on PbO-V₂O₅. Their crystallographic parameters are determined by powder X-ray diffraction. Fe_{1 ? x} Ga _x VO₄ single crystals (x = 0?C0.3) with a volume more than 1cm³ are grown using the seeding technique. The temperature and field dependences of magnetization and magnetic susceptibility of the grown Fe_{1 ? x} Ga _x VO₄ and Fe_{1 ? x} Al _x VO₄ single crystals (x = 0.3 in the solution-melt) are reported. It is shown that the magnetizations of these crystals exceed that of FeVO₄, and both of their antiferromagnetic phase transitions are shifted to lower temperatures.     

Determination of Concentration of Rare Earth Ions Yb3+, Er3+, Tb3+, Ho3+, Tm3+ in Monocrystals of Yttriumaluminum Garnets on Basis of Magnetic Susceptibility

Crystals of solid solutions (R_xY_1-x)₃Al₅O₁₂ (where R is rare earth ion Er³⁺, Yb³⁺, Tb³⁺, Ho³⁺, Tm³⁺) with garnet structure were grown. The temperature dependencies of magnetic susceptibility for these crystals were obtained. On the basis of measurement of magnetic susceptibility a non-destructive technique for determining the concentration of rare earth ions in yttrium-aluminum garnets was developed.     

Diamagnetic and photoabsorption characterisation of gel‐grown cadmium oxalate single crystals

Perfect single crystals of cadmium oxalate trihydrate have been grown using the slow and controlled reaction between Cd⁺² and (C₂O₄)^‐2 ions in agar‐agar gel, resulting in the formation of insoluble product Cd(COO)₂.3H₂O. The optimum growth parameters have been determined. The variation of magnetic moment of the grown crystals under an applied static magnetic field is studied and the material is found to be diamagnetic. The polarizability is found sensitive to optical band gap. An empirical relation between magnetic susceptibility and electronic polarizability has been established. Optical absorption spectra of the sample recorded in the range 200‐2500 nm reveal transitions involving absorption and emission of phonons. The detailed study supports the existence of allowed direct and indirect allowed gaps in the material. The direct allowed transition prevails in the region of relatively higher photon energy. Some feeble disorder in the crystal is conceived to be present. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and magnetic properties of the copper coordination polymer [Cu(µ ‐C2O4)(4‐aminopyridine)2(H2O)]n

In this paper, we consider various ways of crystal growth of the polymer [Cu(µ ‐C₂O₄)(4‐aminopyridine)₂(H₂O)]_n. Single crystals of the size of 1.5×1.5×0.2 mm³ have been grown by a slow diffusion technique from solutions of the monoammine copper complex and of the mixture of potassium oxalate and aminopyridine with the stoichiometric ratio. Magnetic susceptibility and ESR measurements have been performed on single crystals large enough for investigating anisotropic properties. The susceptibility can be well described within the model of a Heisenberg antiferromagnetic spin chain. The magnetic measurements reveal a small concentration of paramagnetic moments reflecting the high quality of the single crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Floating-zone growth of large high-quality CoAl2O4 single crystals

We report the first successful floating-zone growth of high-quality CoAl₂O₄ single crystals with volume up to 1 cm³ free from inclusions and sub-grains. The neutron rocking curves of the CoAl₂O₄ crystal have the width of about 0.30 degree proving the excellent quality of the grown samples. X-ray synchrotron experiments show that crystals have spinel structure with the lattice constant a₀=8.09853(1) Å. Magnetization measurements give the effective magnetic moment μ_eff=4.63 μ_B per Co⁺² ion in a good agreement with previous measurements on ceramic samples.     

Dislocations in magnetic garnet crystals

1. Dislocations in magnetic flux-grown garnet crystals (Y₃Fe₅O₁₂ and others) have been observed. As a rule, {110} growth pyramids have more defects than {211} ones. 2. The highest content of defects (dislocation density 10³–10⁴ cm⁻²) is observed in Y₃Fe₅O₁₂ that grows on crucible walls adjacent to the free surface of the solution where the flow of heat is not uniform to the greatest degree. Bottom grown crystals usually have less dislocations. Far fewer dislocations are in wall grown crystals, least of all dislocations are contained in crystals that grow inside the solution. The solution pouring off at the end of the crystallization period increases dislocation density by some dozens. 3. Heat treatment decreases dislocation density. The less dislocation content and the lower ordering are in the initial crystal, the higher heat treatment effectiveness.     

Growth of (CH3)2NH2CuCl3 single crystals using evaporation method with different temperatures and solvents

The bulk single crystals of low-dimensional magnet (CH₃)₂NH₂CuCl₃ (DMACuCl₃ or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 °C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of X-ray diffraction, specific heat and magnetic susceptibility.     

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr₁₄Cu₂₄O₄₁ show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. T_c onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with T_c max=9.4 K and T_N=5 K at 56 kbars.     

Geometrically frustrated Kagome staircase lattice with chemical disorder

The effect of nonmagnetic Mg²⁺ and magnetic Co²⁺ doping in Kagome staircase compounds was investigated using DC magnetic susceptibility. The main effect of doping is to change effective anisotropy of the Ni₃V₂O₈ and Co₃V₂O₈ crystals. It has a considerable effect on magnetic field induced phase transitions in both kinds of crystals. The doping has also an effect on the Dzyaloshinskii–Moriya exchange interactions. In some cases the doping enhances this interaction while in another it suppresses it completely.     

Single crystal growth from the melt and magnetic properties of hexaferrites–aluminates

Single crystals of aluminum substituted barium hexaferrite were grown by the floating zone method with optical heating. Single crystals were produced from a melt of stoichiometric composition. The process was carried out under a pressure of 50 atm of oxygen. In the system BaO–(x)Al₂O₃–(6?x)Fe₂O₃ the region of single phase crystal growth from the melt is limited by the value x=3. For higher substitutions single-phase crystallization is not observed. The grown single crystals are cylindrical boules with a diameter of 4–5 mm and with lengths up to 50 mm. To avert cracking the crystals have been annealed during the process of growth at 1100 °C. The content of FeO in the composition of single crystals of barium hexaferrite, grown by zone melting under an oxygen pressure of 50 atm, is approximately 0.3 wt%. In the system of hexaferrite–aluminates the macroscopic magnetic moment of the material disappears at x=3.     

Growth and characterization of titanium suboxide crystals

The titanium and vanadium suboxides MO_x (where 1.5 < x < 2 and M is Ti or V) are particularly interesting compounds because many show metal-insulator transitions which result in interesting electrical, magnetic and spectroscopic phenomena. We have grown high purity crystals of the congruently melting compounds Ti₂O₃, Ti₃O₅ and V₂O₃ and mixed compounds using the tri-arc melting technique. Crystals were grown at speeds of 1-1.5 cm/h. The Magneli phases M_nO_2n-1 (n?4) do not melt congruently and therefore we have grown a number of these compounds using chemical vapor transport with TeC1₄ or NH₄C1. Twinned needles typically larger than 1 cm long are grown by pulling transport in 3–5 days. The crystals have been characterized by X-ray diffraction, atomic absorption and gamma-ray activation analysis. In addition, the use of a scanning microcalorimeter made it possible to determine phase transitions on needles weighing as little as 2–10 mg. The stoichiometry was determined using X-ray diffraction, pycnometric density measurements and thermogravimetry.     

Synthesis and characterization of ferroelectric magnesium hydrogen phosphate single crystals

Ferroelectric Magnesium Hydrogen Phosphate MgHPO₄ (MHP) single crystals are grown by slow diffusion of magnesium chloride in sodium metasilicate gels impregnated with orthophosphoric acid. Bright and transparent prismatic, tabular, and isometric habit MHP crystals upto 3 × 2 × 1 mm³ are obtained. Results of chemical, X-ray diffraction, EDAX, microhardness and magnetic analysis are reported. The average etch pit density is determined by chemical etching to be 7 × 10³ cm⁻². Microtopographic investigations revealed the mechanism of crystal growth.     

Magnetic and magnetostrictive behavior of Dy3+ doped CoFe2O4 single crystals grown by flux method

We studied the effect of Dy³⁺ content on the magnetic properties of cobalt ferrite single crystal. The single crystals of CoFe_1.9Dy_0.1O₄ were grown by the flux method using Na₂B₄O₇.10 H₂O (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction analysis at room temperature confirmed the spinel cubic structure with lattice constant a=8.42 Å of the single crystals. The compositional analysis endorses the presence of constituents Co, Fe and Dy elements after sintering at 1300 °C within the final structure. The magnetic hysteresis measurements at various temperatures viz. 10 K, 100 K, 200 K and 300 K reveal the soft ferrimagnetic nature of the single crystal than that of for pure CoFe₂O₄. The observed saturation magnetization (M_s) and coercivity (H_c) are found to be lower than that of pure CoFe₂O₄ single crystal. The magnetostriction (λ) measurement was carried out along the [001] direction. The magnetic measurements lead to conclude that the present single crystals can be used for magneto-optic recording media.     

Single crystal growth and physical properties of superconducting ferro-pnictides Ba(Fe,Co)2As2 grown using self-flux and Bridgman techniques

We have employed the high temperature solutions growth technique and the Bridgman technique to grow cm-size high-quality single crystals of pristine BaFe₂As₂ (Ba122) and its Co-doped superconducting variants. In the first approach, self-flux (Fe, Co)As was used to achieve a homogeneous melt of composition Ba(Fe, Co)_3.1As_3.1 at T=1463 K. The melt was then cooled slowly under a temperature gradient in a double-wall crucible assembly to obtain large and flux-free single crystals of Ba(Fe, Co)₂As₂. In the second approach, single crystals were grown directly from a stoichiometric Ba(Fe, Co)₂As₂ melt at T=1723 K employing the Bridgman technique associated with a vertical tube furnace. Using both techniques single crystals with lateral dimensions up to 25×10 mm² and thickness up to 1 mm were obtained. Details of the two methods are given and a comparative study of the magnetic and transport properties of the single crystals obtained using the two methods is presented.     

Growth and study of PbFe1/2Ta1/2O3 single crystals

Single crystals of the composition PbFe_1/2Ta_1/2O₃ are grown by the method of mass crystallization from flux. It is established that, unlike the PbFe_1/2Ta_1/2O₃ ceramic, the synthesized single crystals possess pronounced relaxor properties: the maximum of the dielectric constant is diffuse and its temperature, T _m, increases by more than 70 K with an increase in the frequency from 10² to 10⁶ Hz. It is assumed that the unusual properties of the PbFe_1/2Ta_1/2O₃ crystals are caused by mesoscopically inhomogeneous compositional ordering and comparatively high conductivity providing favorable conditions for the appearance of the volume-charge and thermal electron polarization.     

Magnetic Moment and Susceptibility Measurements of Mixed Rare Earth Oxalate Crystals

The growth of double rare earth oxalate crystals with a general chemical formula AB(C₂O₄)₃ · 10 H₂O (where A and H are Nd, Pr and Sm) is reported. The variation of the magnetic moment of these crystals with an external field is studied and the magnetic susceptibility and the effective magnetic moment are calculated. The observed effective magnetic moment of the crystals are in good agreement with those calculated on theoretical grounds.     

Synthesis and X-ray diffraction study of K2.92Nb2.58Ti1.42P2.5O17 single crystals

Single crystals of the composition K_2.92Nb_2.58Ti_1.42P_2.5O₁₇ possessing ionic conductivity σ = 10³ Ω cm^?1 at 300°C were grown by the method of spontaneous crystallization from flux in the quaternary K₂O-TiO₂-Nb₂O₅-P₂O₅ system. The X-ray diffraction study of the single crystals grown showed that they are monoclinic with the unit-cell parameters a = 13.800(1), b = 6.412(2), c = 16.893(3) Å, β = 83.33(1)°, Z = 16, sp. gr. P2/n and provided the determination of the structure of this new compound. The Nb and Ti atoms statistically (with different probabilities) occupy four crystallographically independent octahedra. The (Nb,Ti) and P-tetrahedra form the three-dimensional framework with the channels along the diagonal [101] direction occupied by potassium atoms.     

Magnetic susceptibility of sodium rare-earth fluorites Na0.5 − x R 0.5 + x F2 + 2x (R = Dy, Ho, Er, Tm, Yb) and some ordered phases

Magnetic properties of the nonstoichiometric phases with the fluorite-type “defect” structure Na_0.4 R _0.6F_2.2 (R = Ho, Er, Tm, Yb) and Na_0.35Dy_0.65F_2.3 have been studied as well as some ordered phases with different distortions of the initial fluorite lattice (NaHo₂F₇, Na₇Tm₁₃F₄₆, NaYb₂F₇, and Na₇Yb₁₃F₄₆) and Na_1.5Dy_1.5F₆ with the gagarinite-type structure (NaCaYF₆). Magnetic susceptibility χ was measured with the aid of the Faraday balance in the temperature range from 20 to 300 K. The crystals with R= Dy, Ho, Er, Tm are paramagnetic; their temperature dependence χ is described by the Curie-Weiss law. It is shown that in the temperature range studied, magnetic susceptibility does not depend on the degree of order of Dy, Ho, Er, and Tm ions in the structure. Below 80 K, the temperature dependence of magnetic susceptibility of the the Yb³⁺-containing phases differs from the analogous dependence χ of an ideal paramagnetic crystal, which is assumed to be caused by the interaction of the crystalline field with Yb³⁺ ions.     

Recombinant formate dehydrogenase from <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>: Preparation,crystal growth in microgravity,and preliminary X-ray diffraction study

Crystals of high-purity recombinant NAD⁺-dependent formate dehydrogenase from the higher plant Arabidopsis thaliana (AraFDH) were grown in microgravity in the Modul’-1 protein crystallization apparatus on the International Space Station. The space-grown crystals have larger sizes than those grown on Earth. X-ray diffraction data suitable for determining the three-dimensional structure were collected from the space-grown crystals to a resolution of 1.22 Å using an X-ray synchrotron source. The crystals belong to sp. gr. P4₃2₁2; the unit-cell parameters are a = b = 107.865 Å, c = 71.180 Å, α = β = γ = 90°.