Low temperature structural distortion in the high Tc Chevrel-phase superconductors PbMo6S8 and SnMo6S8

High-resolution powder neutron diffraction data reveal that, at temperatures below 100 K, oxygen-free, high-T_c samples of PbMo₆S₈ and SnMo₆S₈ exhibit a small structural distortion from the R$\text{3}$ rhombohedral space group. The data cannot be refined in a simple P$\text{1}$ triclinic space group as previously reported for EuMo₆S₈ and BaMo₆S₈. Thus, a supercell ordering is suggested.     

三元化合物SnMo6S8的超导转变温度与电子态密度

本文给出,当氧含量增加时,三元化合物SnMo₆S₈的Pauli顺磁磁化率下降。利用BCS理论,由磁化率的变化导出的临界温度的变化与实验符合。 关键词：     

Domain wall structure and the properties of the coexistence phase in ferromagnetic superconductors HoMo6S8 and HoMo6Se8

In the framework of Ising ferromagnetic model the temperature dependence of the domain wall surface energy is studied. The obtained results are used to calculate the temperature dependence of the wave vector of the oscillatory magnetic structure in the coexistence phase of ferromagnetic superconductor HoMo₆Se₈. The estimate of the exchange interaction of localized moments and electrons explains why the coexistence phase survives on cooling down to zero temperature in HoMo₆Se₈ while the reentrant transition into the normal ferromagnetic phase takes place in HoMo₆Se₈.     

Pressure induced superconductivity in BaMo6S8

The resistance and a.c. magnetic susceptibility of BaMo₆S₈ have been measured under pressure. A resistance-anomaly, indicative of the reported structural transformation at ～ 145 K, was observed. Non-bulk superconductivity with a pressure dependent signal size was induced by a quasi-hydrostatic pressure ? 15 kbar but not a hydrostatic pressure up to 18 kbar down to 1.2 K.     

Critical currents of LaMo6S8 thin films

The thin films of LaMo₆S₈ were prepared by d.c. getter sputtering method. Critical current have been measured vs applied magnetic field B_⊥ up to 8 T at the temperature ranged from 1.7 to 4.2 K. The highest critical current density reached was J_c = 1.7 × 10⁷ Am^?2 at B = 0 and T = 1.7 K. Based on the measurements performed, it was possible to indicate that depending on the heat treatment applied, the pinning forces created in the LaMo₆S₈ thin films obey the scaling law.     

Superconductivity in the RexMo6S8

The rare earth molybdenum sulfides RE_xMo₆S₈ (RE = rare earth) have been synthesized and are found to be superconducting with a few exceptions. This result, which is surprising in view of the high concentration of magnetic ions, is correlated with the particular structure of these compounds based on on units of Mo₆S₈.     

Lattice instability in the non-superconducting compound EuMo6S8

We have performed electrical resistivity and specific heat measurements on bulk Eu_1.1Mo₆S₈ together with low-temperature X-ray powder diffractometry. These investigations revealed a structural phase transition (occuring at 109 K) from the room-temperature rhombohedral structure to a low-temperature triclinic distorted structure in which the compound exhibits a non-metallic behavior.     

Nuclear spin-lattice relaxation of V in TIxV5S8 and TIxV6S8

Temperature dependence of the nuclear spin-lattice relaxation rate of ⁵¹V has been studied in metallic vanadium sulfides with quasi-one-dimensional structures. The ternary sulfide TI_0.54V₅S₈ is suggested to be an exchange-enhanced Pauli-parammagnet with antiferromagnetic correlation.     

Superconducting thin films of MxMo6S8 type

Thin films of M_xMo₆S₈, where M=Pb, Sn, Sn-Al and Cu, known as the Chevrel phases have been prepared by d.c. getter sputtering method and the optimal conditions of their preparation have been determined. The transition temperatures reached: 10.16, 13.66, 11.74 and 12.86 K for thin films with M=Cu, Sn, Sn-Al and Pb respectively. The highest critical fields H_c²(0) of 428 kG were obtained for Pb compounds.     

Magnetic structure of V5S8

The magnetic structure of V₅S₈ has been investigated by neutron diffraction at low temperature. Two single crystals (sample 1 and sample 2) grown by the same procedure gave considerably different results. Sample 1 was found to have an incommensurate structure, while sample 2 was found to have simple collinear antiferromagnetic structure consistent with magnetic measurements. Although the positions of the magnetic diffraction peaks of sample 1 were close to those of sample 2, the neutron intensity behavior was quite different and the detailed structure could not be determined in the case of sample 1. In both samples, the magnitude of the moments was evaluated to be much larger than the value estimated from NMR.     

Neutron diffraction study of the magnetic order in the ternary superconductor GdMo6S8

The coexistence of antiferromagnetism and superconductivity has been demonstrated in GdMo₆S₈ by neutron diffraction experiments. Although the magnetic unit cell (2a,a,a) is determined by the RKKY interactions, the direction of magnetic moments is determined by the anisotropic dipolar interactions i.e. in the (100) cubic plane.     

Domain-like magnetic structure in superconductors of ErRh4B4 and HoMo6S8 type

The problem of the coexistence of superconductivity and magnetic order is studied by taking into account the indirect exchange interaction, magnetic dipolar interaction and magnetic anisotropy. It is shown that the domain-like magnetic structure should be realized in the superconducting phases of ErRh₄B₄ and HoMo₆S₈ at the temperatures T_m = 1.4 and 0.7 K respectively. The transition from superconducting domain-like phase (DS) to the normal ferromagnetic (FN) state is described.     

A triple potential model for the structural transition in Cu2Mo6S8

A simple model for the structural phase transition in Cu₂Mo₆S₈ is proposed. The model uses a triple well potential for copper atoms. In the molecular field approximation a first order transition of the order—disorder type involving the rearrangement of the copper atoms is obtained.     

Direct observation of long range ferromagnetic order in the reentrant superconductor HoMo6S8

The neutron scattering technique has been used to investigate the magnetic properties of the ternary Chevrel-phase superconductor HoMo₆S₈. Magnetic critical scattering is observed in the superconducting phase, with the magnetic correlation range increasing with decreasing temperature. At the transition in which the normal state is reentered, the system is found to develop long range ferromagnetic order, with a saturated magnetic moment at low temperatures of 9.06 ± .3 μ_B and the spin direction along the unique [111] trigonal axis.     

Spin structure and magnetic anisotropy of Cr5S6 and rhombohedral Cr2S3

The magnetic properties of single crystals of rhombohedral Cr₂S₃ have been measured. The data indicate a preferred orientation of the spins of the Cr atoms in a plane perpendicular to the trigonal axis. New neutron diffraction data for powdered samples which confirm this conclusion are presented.     

Synthesis and physical properties of new superconducting Chevrel phases HgxMo6S8

New ternary molybdenum chalcogenides Hg_xMo₆S₈ (0 < x < 1) have been synthesized and investigated for their structural, magnetic, and superconducting behavior. These new phases prepared at low temperature by reaction of mercury with Mo₆S₈ (obtained from oxidation of Cu₂Mo₆S₈ by iodine) have been characterized by x-ray diffraction, static Faraday susceptibility, and superconducting transition temperature studies. HgMo₆S₈ crystallizes in the rhombohedral space group $\text{R}\text{3 (}\text{a}{}_{\mathrm{r}}\text{= 6.51}\text{A}\text{?}\text{, α}{}_{\mathrm{<mtext>r</mtext>}}\text{= 92.53°)}$, has a paramagnetic, temperature dependent susceptibility, and superconducts at 8.1K. As the mercury content decreases, a continuous decrease in T_c from 8.1K to 1.7K for x=0 (Mo₆S₈) is observed.     

Magnetic properties of V5S8 single crystals

The magnetic properties of V₅S₈ single crystals have been investigated by susceptibility and torque measurements. The susceptibilities parallel and perpendicular to the magnetic easy axis show a remarkable anisotropy below the Neel temperature of 32 K and are nearly Isotropie above that temperature. The easy axis is found to be nearly along the c-axis of the monoclinic lattice, being inclined at an angle of 9.6 ± 1.0° from the c-axis toward the a-axis. The torque curves, measured up to 24.4 kOe at liquid helium temperature, deviate from the usual form of a sine function with increasing magnetic field. The analysis of these torque curves suggests that spin flopping may occur at 43 kOe, a comparatively low critical field. Using these experimental results, a localized d-electron model for a particular site of the vanadium-ion, proposed by previous investigators, is examined.     

A neutron diffraction study of the coexistence of antiferromagnetism and superconductivity in GdMo6S8

The present neutron diffraction study confirms that GdMo₆S₈ orders antiferromagnetically in the superconducting state at a Néel temperature T_N = 0.84 K. Previous neutron scattering studies have demonstrated the coexistence of antiferromagnetism and superconductivity in two other rare earth ternary compounds, DyMo₆S₈ and TbMo₆S₆.     

反应扩散法制备的PbMo6S8超导带的超导特性

本文报道反应扩散法制备Chevrel相PbMo₆S₈超导带材的过程以及带材的超导特性。Mo带与H₂S气体反应生成单相的Mo-S化合物(MoS₂或Mo₂S₃,根据反应温度而定),再与Pb的蒸汽反应生成单相的PbMo₆S₈薄层。PbMo₆S₈超导层的临界温度T_c=13.0 关键词：     

Physcio-chemical properties of the non-stoichiometric VS2 and V5S8 phases

Density, Laue back-reflection and powder X-ray measurements have confirmed a previous structural determination of the VS₂-phase. Measurements of the temperature dependence of the magnetic susceptibility and electrical resistivity of VS₂ in the temperature range 100–300°K give evidence that in this structure, as in V₅S₈, there are V atoms with both localized and delocalized d-electrons leading to a paramagnetic susceptibility containing a temperature-independent component and a component in which the permanent magnetic dipoles give rise to a Curie-Weiss behavior.