Relationship between the crystal structure and the reentrant superconducting properties of (Sn1-xErx)Er4Rh6Sn18

Single crystals of (Sn_1-xEr_x)Er₄Rh₆Sn₁₈ are superconducting (T_c = 1.3K) for x 0, are reetrant superconducting (T_c = 1.24K and T_M = 0.34K) for x ～.30 and undergo a singel magnetic transition (T_M=0.68K) for x～.75. Since the occupancy of the [Sn(1)_1-xEr(1)_x]Er(2)₄ sublattice is responsible for the variation of the low-temperature properties, one can make predictions as to new reentrant superconductors in the MRh_xSn_y series (M=RE). This appears to be the first system of reentrant superconductors where stoichiometry within a sublattice controls both magnetic ordering and superconductivity.     

Magnetic phase transitions in Nd7Rh3 single crystal

Magnetic phase transitions in rare earth intermetallic compound Nd₇Rh₃ have been investigated using a single crystal. Measurement results of magnetization, magnetic susceptibility, specific heat, and electrical resistivity reveal that Nd₇Rh₃ has two magnetic phase transitions at T_N=34 K, T_t2=9.1 K and a change of the magnetic feature at T_t1=6.8 K in the absence of an external magnetic field. Antiferromagnetic orderings exist in all the three magnetic states; a large magnetic anisotropy between the c-axis and the c-plane is observed. In the magnetic phase below T_t2, an irreversible field-induced magnetic phase transition takes place in the c-plane; after removing external magnetic field, a coexistence state of ferro- and antiferromagnetic ordering or a ferrimagnetic state having a remanent magnetization M_R is stabilized. The M_R decays to a certain value for several hours after the first process; a magnetic field cooling effect was also observed in the c-plane below T_t2. In the antiferromagentic state above T_t2, the irreversibility disappears and an ordinary antiferromagnetic state takes place. As the origin of this phenomenon, a kind of martensitic structural transition that is observed in Gd₅Ge₄ can be considered.     

Irreversible magnetovolume effect in Nd7Rh3 single crystal

Magnetovolume effect in Nd₇Rh₃ single crystal has been studied by measuring the magnetostriction as a function of external magnetic field at 4.2 K. An irreversible magnetovolume effect having a negative remanent volume magnetostriction was observed when the external magnetic field was applied along the b-axis. The irreversible magnetostrictive effect takes place in the longitudinal magnetostriction along the b-axis. The remanent magnetostriction along the b-axis relaxes after removing external magnetic field for several hours and equilibrium state is stabilized.     

Cu NMR study of the superconducting thiospinel Cu1.5Rh1.5S4

The ⁶³Cu NMR Knight shift K and spin-lattice relaxation rate 1/T₁ have been measured to study the thiospinel superconductor Cu_1.5Rh_1.5S₄ from a microscopic viewpoint. K is negative and has a weak dependence on temperature, and the hyperfine coupling constant H_hf^d is estimated to be −52.4 kOe/μ_B. 1/T₁ is proportional to the temperature in the normal state. In the superconducting state, 1/T₁ takes a coherence peak just below T_c, and decreases exponentially well below T_c, from whose temperature dependence the superconducting energy gap has been proved to be close to 2Δ = 3.52k_BT_c given by the BCS theory.     

Magnetic structure of the new perovskite-like ferrimagnet ThCu3Mn4O12

Magnetic properties of polycrystalline samples in the perovskite-like compound ThCu₃Mn₄O₁₂ (space group Im 3) have been investigated by neutron diffraction, magnetization and susceptibility measurements. This compound is ferrimagnetic with a colinear spin configuration, below T_c = 430 K; at 4.2 K the spontaneous magnetization is 9.5 μ_B/f.u. The colinear structure is stabilized by a strong antiferromagnetic coupling between copper and maganese cations.     

Laser oscillation of a LiPrP4O12 single crystal

We report on pulsed laser action in a LiPrP₄O₁₂ single crystal at room temperature. A simultaneous laser operation at the wavelengths of λ₁ = 604.8 nm, λ₂ = 608.5 nm, λ₃ = 639.6 nm, and λ₄ = 720.4 nm was observed. Spectroscopic properties of the LiPrP₄O₁₂ crystal are briefly described.     

Spectroscopic investigation of a new crystal： Nd^3＋,Yb^3＋：YVO4

The absorption and emission spectra of the YVO4 single crystal co-doped with 1 at.% Nd^3＋ and 1 at.% Yb^3＋ are investigated. The efficient Nd^3＋ → Yb^3＋ energy transfer and the back transfer （Yb^3＋ → Nd^3＋） are observed at room temperature. The fluorescence lifetime of the 4F3/2 level of Nd^3＋ in Nd,Yb：YVO4 is measured under 808 nm laser light excitation. The efficiency of Nd^3＋ → Yb^3＋ energy transfer in YVO4 is determined to be about 34%.     

The crystal structure, magnetism, and colossal magnetoresistance of Y2CrS4

Ternary yttrium chromium sulfide,Y2CrS4,prepared by the solid-state reaction of Y2S3,Cr,and S,was found to exhibit an antiferromagnetic transition at about 64 K.The X-ray diffraction pattern at 300 K was refined with space group Pca2 1,and the structure parameters were determined to be a = 12.51 Ab = 7.53A,and c = 12.49A,We investigated the magnetotransport properties,and observed negative colossal magnetoresistance reaching up to 2.5 × 10^ 4 % in the semiconducting compound of Y2CrS4.     

180° domain structure in a cubic U3P4 crystal

In a thick plate cut from a U₃P₄ single crystal perpendicularly to the 111 direction, changes in the domain structure under the influence of a strong magnetic field perpendicular to the plate surface were studied. Experiments were carried out at T = 28 K, applying the Kerr effect technique to make the domain structure visible. In the cubic crystal studied, the applied field was found to force the appearance of a 180° branched maze domain structure, typical of thick plates of highly anisotropic uniaxial materials. The Hubert-Bodenberger model of this structure was improved and extended by considering the change in the shape of domains occurring with increase in the distance from the sample surfaces, by describing the sample in a non-zero magnetic field and by analyzing the sample in the state of remanence. The model was applied to the case of U₃P₄ and the energy density of 180° domain walls was estimated (γ = 12 erg/cm²).     

Magnetic anisotropy and geometrical frustration in the Ising spin-chain system Sr5Rh4O12

A structural and thermodynamic study of the newly synthesized single crystal Sr₅Rh₄O₁₂ is reported. Sr₅Rh₄O₁₂ consists of a triangular lattice of spin chains running along the c-axis. It is antiferromagnetically ordered below 23 K with the intrachain and interchain coupling being ferromagnetic (FM) and antiferromagnetic (AFM), respectively. There is strong evidence for an Ising character in the interaction and geometrical frustration that causes incomplete long-range AFM order. The isothermal magnetization exhibits two step-like transitions leading to a ferrimagnetic state at 2.4 T and a FM state at 4.8 T, respectively. Sr₅Rh₄O₁₂ is a unique frustrated spin-chain system ever found in 4d and 5d based materials without a presence of an incomplete 3d-electron shell.     

Investigation on intracavity second-harmonic generation of a new Li-doped GdCa4O(BO3)3 crystal

Efficient intracavity second-harmonic generation (SHG) has been realized in a new Li-doped GdCa₄O(BO₃)₃ (GdCOB) crystal. 2.55 W CW SHG output power was obtained with an optical conversion efficiency of 19.6%, while the effective intracavity SHG efficiency was determined to be 44%. Compared to that of undoped GdCOB crystal, the effective SHG efficiency of the Li-doped GdCOB crystal was found to increase by 12.5%.     

Th3Ni2B2N3 a possible new superconducting compound: insights from electronic band structure

La₃Ni₂B₂N₃, which is similar to YNi₂B₂C and related borocarbides, was earlier studied by the electronic structure calculations [D.J. Singh, W.E. Pickett, Phys. Rev. B 51 (1995) 8668.], and was predicted to be a 3-D metal. In search of new compounds of the borocarbide and related families to get higher T_C, we have studied the compound Th₃Ni₂B₂N₃, by the first principles full potential electronic structure calculations by the linear augmented plane wave method. We get similar band structure for Th₃Ni₂B₂N₃ as found for La₃Ni₂B₂N₃, and the various atom-split component density of states show similar properties. The total electron density of states at Fermi level has been increased to about 92 states per Ry per f.u. as compared to 57 states per Ry per f.u. in La₃Ni₂B₂N₃. The main increase is due to the increased hybridization of the 5f states as seen by the more prominent low energy tail in the Th-component density of states. Based on this enhancement we predict Th₃Ni₂B₂N₃ to be a high temperature superconductor with a T_c in excess of 30 K.     

Absence of hydrogen in superconducting molybdenum sulfide,Mo3S4

Superconducting Mo₃S₄(T_c=1.8 K) was prepared from the ternary sulfides MMo₃S₄ (M=Cu, Ni) by the acid extraction method, and was studied by neutron diffraction and NMR spectroscopy. In contrast to earlier reports no significant amounts of hydrogen could be found in the rhombohedral structure. However, large proton concentrations were found in samples which had been exposed to moist air.     

Electronic structure and the infrared absorption and Raman spectra of the semiconductor clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12

The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor clusters C₂₄, B₁₂N₁₂, Si₁₂C₁₂, Zn₁₂O₁₂, and Ga₁₂N₁₂ are calculated using the ab initio Hartree-Fock method in the 6–31G basis set. Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3, pp. 535–542.     

Superconducting Dy(IrxRh1−x)4B4 system

The boundaries between the paramagnetic, superconducting and magnetically-ordered phases in the pseudoternary system Dy(Ir_xRh_1?x)₄B₄ have been established down to 1.2 K. Comparisons between the present system and other pseudoternary systems M(Ir_xRh_1?x)₄B₄ show that the depression of the superconducting transition temperature (ΔT_c), relative to the nonmagnetic Lu compounds, can be described qualitatively by the de Gennes factor (g?1)²J(J+1). The nature of the magnetic order for the Rh-rich compounds was investigated by means of low field measurements and seems to be different from simple ferromagnetism.     

Synthesis and crystal structure of [3,5-(CH3)2C6H3NH3]4P4O12·3H2O

Chemical preparation and crystal structure are given for a new cyclotetraphosphate: [3,5-(CH₃)₂C₆H₃NH₃]₄P₄O₁₂·3H₂O. This compound is triclinic P with the following unit-cell parameters: a=8.298(3), b=8.299(3), c=17.242(7)Å, α=97.13(3), β=102.72(3), γ=64.55(3)°, Z=1 and V=1045.2(8)ų. The crystal structure has been solved and refined to R=0.040 using 6086 independent reflections. The atomic arrangement can be described as layers organization. Layers built by P₄O₁₂ ring anions, ammonium groups and water molecules parallel to the plan (001), between which the organic groups are located. Characterization by X-ray diffraction, IR absorption, and thermal analysis are described.     

The elastic behaviour of the ternary zincblende structure semiconductor CuGe2P3

A single crystal has been grown of CuGe₂P₃, a ternary semiconductor with a zincblende structure in which the copper and germanium atoms are randomly distributed on the cation sites. The second order elastic constants measured by the ultrasonic pulse echo overlap technique (C₁₁ = 13.66, C₁₂ = 6.17, C₄₄ = 6.66 and bulk modulus B = 8.67 in units of 10¹⁰Nm^?2 at 291 K) are closely similar to those of GaP and conform well to Keyes' correlation for zincblende structure crystals. The hydrostatic pressure derivatives of the second order elastic constants ($\text{?C}{}_{11}\text{?P}\text{= 4.40}$, $\text{?C}{}_{12}\text{?P}\text{= 3.9}$, $\text{?C}{}_{44}\text{?P}\text{= 0.93}$ and $\text{?B}\text{?P}\text{= 4.07}$) and the third order elastic constants (C₁₁₁ = ? 8.45, C₁₁₂ = ? 3.49, C₁₂₃ = ? 1.13, C₁₄₄ = ? 2.82, C₁₅₅ = ? 1.44 and C₄₅₆ = ? 0.69 in units of 10¹¹Nm^?2) also resemble those of GaP: even the anharmonicity of the long wavelength acoustic modes of this ternary semiconductor resembles that of its binary “parent” compound. The positive signs of the hydrostatic pressure derivatives and the negative signs of the third order elastic constants show that the acoustic modes at the long wavelength limit stiffen under pressure, an effect which is quantified here by computation of the mode Grüneisen parameters, which are all positive. The harmonic and anharmonic force constants, obtained in the valence force field model, fit well into the pattern shown by related zincblende structure compounds: the ratio ($\text{β}\text{α}$) for bond bending (β) to stretching (α) force constants is greater than 4:1; the dominating anharmonic force constant is γ: most of the anharmonicity is associated with nearest neighbour atoms. Analysis of the temperature dependence of the elastic constants on the basis of a simple anharmonic model again emphasises the similarity between the elastic behaviour of CuGe₂P₃ and GaP. The thermal expansion of CuGe₂P₃ varies almost linearly with temperature between 291 K and 1000 K, the linear coefficient of thermal expansion α being 8.21 ± 0.02 × 10^?6 °C^?1. The similar lattice parameters and elastic behaviour of CuGe₂P₃ and GaP indicate that semiconducting devices made of epitaxial deposits of CuGe₂P₃ on a GaP substrate should prove to be almost strain-free.     

Neutron diffraction studies of Tb2Rh3Si5 compound

In this work neutron diffraction studies of Tb₂Rh₃Si₅ compound are reported. The compound crystallizes in the monoclinic crystal structure of Lu₂Co₃Si₅-type. At 1.5 K an antiferromagnetic ordering with a propagation vector k=(1/2;1/2;1/2) was observed. The Tb magnetic moments of 9.8(2) μ_B form a non-collinear magnetic structure. In the vicinity of Néel temperature of 8 K a change of the magnetic ordering is evidenced. The change seems to be connected with phase transition from commensurate to incommensurate sine-wave modulation of the Tb magnetic moments.     

Non-colinear magnetic structure of U3P4 and U3As4

Neutron diffraction experiments have been performed on single crystal samples of U₃P₄ and U₃As₄. The magnetic ordering is found to be a non-collinear three axial structure in which magnetic moments of U⁴⁺ ions are tilted from the [111] axis by an angle of about twenty degrees within (110) planes.     

The Yb to Er energy transfer in YAl3(BO3)4 crystal

The Yb³⁺ to Er³⁺ energy transfer in yttrium aluminum borate (YAB) crystal is investigated with the rate equation without considering the back energy transfer. The energy transfer coefficients (W₂₅) in the crystals with different Yb³⁺ concentrations are determined and compared with those in other crystals. The transfer efficiencies and the micro-parameters of energy transfer and migration are also determined. The results show that the energy transfer from Yb³⁺ to Er³⁺ in YAB crystal is very efficient and the Yb³⁺–Er³⁺ co-doped YAB crystal may be a good candidate for the 1.55 μm laser media.