Reentrant superconductivity in the orthorhombic system (Tm1−xLux)RuB2

The boundaries between the paramagnetic, superconducting and magnetically ordered phases in the orthorhombic pseudoternary system (Tm_1?xLu_x)RuB₂ have been established by means of ac magnetic susceptibility measurements down to 1.2 K. Reentrant superconductivity occurs between x = 0.52 and x ? 0.68. The absence of coexistence between superconductivity and long range magnetic order in this region suggests a ferromagnetic-like nature of the magnetic state. The initial linear depression of superconducting transition temperature (T_c) gives a coupling constant value N(E_F)$\text{J}$² between conduction electrons and magnetic Tm³⁺ moments of 6.7 × 10^?4 eV-atom-states/ spin direction.     

The magnetic properties of RuF5

The structural unit of the pentafluorides MF₅ (M = Ru, Rh, Os, Ir, Pt) consists of M₄F₂₀ tetramers with the transition elements occupying the corners of the rhombus. In the case of RuF₅ the magnetic susceptibility vs. temperature curve shows a broad maximum at T ? 40 K. Neutron diffraction experiments below and above this temperature show that this maximum does not correspond to a magnetic three-dimensional ordering. Theoretical calculations based on isolated tetra-nuclear clusters of identical $\text{S =}\text{3}\text{2}$ spins have been applied. The intracluster exchange interactions are antiferromagnetic. The fitting of the susceptibility data leads to an exchange constant of $\text{J}\text{k}\text{= ?8.3 K}$.     

Magnetic properties of CuCr2Se4 single crystals

The magnetic properties of CuCr₂Se₄ single crystals, which were grown by chemical transport reactions using iodine as a carrier, have been investigated. The magnetic moment at 0 K is found to be 5.07 μ_B per mole. The susceptibility at high temperatures follows a Curie-Weiss law with an asymptotic Curie temperature 430 K and a Curie constant 2.55 emu · $\text{deg}\text{mol}$. The magnetocrystalline anisotropy constants K₁ and K₂ are ? 6.9x 10⁵ and ? 0.9x 10⁵$\text{erg}\text{cm}{}^3$, respectively, at 5.1 K.In order to examine the effects of annealing on the magnetocrystalline anisotropy, the ferromagnetic resonance at room temperature was measured after annealing in vacuum and subsequently in an atmosphere of Se. It is found that the absolute values of K₁ and K₂ decrease after annealing in vacuum and increase to the initial values after annealing in an atmosphere of Se.     

Compensation effect in an exchange enhanced superconductor: [(La.993Lu.007)1−xGdx]Ru2

We have measured the upper critical field, H_c2, of alloys of the form [(La_.993Lu_.007)_1?xGd_x]Ru₂. For large $\text{(x?0.02)}$ concentrations of Gd, the critical fields are re-entrant. For small (x?0.01) concentrations of Gd, the critical fields cross the pure sample critical fields and rise above them due to compensation of the externally applied magnetic field by the negative effective internal field of the magnetic impurity. Compensation occurs at relatively low fields (25 KG) in this system as a result of substantial exchange enhancement. From the concentration and critical field of the most compensated sample, we find a value for the exchange integral, J(0) = ?(15+?2) meV, and a susceptibility enhancement factor in excellent agreement with EPR, specific heat and static susceptibility measurements.     

Electrical transport and magnetic properties of Nd2(WO4)3

Measurements of the molar magnetic susceptibility (X_m) of a powdered sample of Nd₂(WO₄)₃ in the temperature range 300–900 K, and the electrical conductivity (σ) and dielectric constant (?$\text{)}\text{?}$ of pressed pellets of the compound in the temperature range 4.2–1180 K are reported. X_m obeys the Curie-Weiss law with a Curie constant C= 3.13 K/mole, a paramagnetic Curie temperature θ= ?60 K and a moment of Bohr magnetons, p= 3.49 for the Nd³⁺ ion. The electrical conductivity data can be explained in terms of the usual band model and impurity levels. Both the σ and ?$\text{\$}\text{?}$data indicate some sort of phase transition round 1025 K. The conductivity follows Mott's law $\text{σ = A exp (?B/T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{)}$ in the temperature range $\text{200 < T < 3000}\text{K with}\text{B = 45.00 (}\text{K}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{and}\text{A = 1.38 × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$. The dielectric constant increases slowly up to 600 K, as is usual for ionic solids. The increase becomes much faster above 600 K, which is attributed to space-charge polarization of thermally generated charge carriers.     

Thermal and magnetic studies of the nearly one-dimensional antiferromagnetic system CsNiBr3

Magnetic susceptibility, specific heat and ¹³³Cs magnetic resonance measurements in a single crystal of CsNiBr₃ are reported. The data reveal two magnetic transitions separating the paramagnetic phase from the antiferromagnetic ground state. At the higher transition temperature T_N2 = (14.25 ± 0.05)K a net magnetic moment is observed only along the hexagonal c-axis, while only below the lower transition temperature T_N1 = (11.75 ± 0.05)K a perpendicular component of the magnetic moment appears also. Above T_N2 CsNiBr₃ can be described as a one-dimensional antiferromagnet with intrachain exchange interaction $\text{J}\text{k}{}_{\mathrm{B}}\text{= ?(17.0 ± 0.2)}\text{K}$ and single-ion anisotropy constant $\text{D}\text{k}{}_{\mathrm{B}}\text{? ?1.5}\text{K}$. Below T_N1, the data are consistent with the non-colinear triangular structure of the Ni²⁺ moments proposed previously for the isomorphic crystal CsNiCl₃. A reduced value of the zero-temperature susceptibility over the classical value is found and atrributed to the zero point deviations.     

The antiferroelectric phase transition in TlH2PO4 and TlD2PO4

It is shown by X-ray diffraction measurements that the transitions at 230 K in TlH₂PO₄ and at ≈ 350 K in TlD₂PO₄ are structurally equivalent. In both cases, on cooling through the transition, new reflections appear at points ($\text{h +}\text{1}\text{2}$, $\text{k +}\text{1}\text{2}$, l) referred to the primitive monoclinic unit cell of the high-temperature phase. In TlH₂PO₄ some distinct but broadened scattering remains at the ($\text{h +}\text{1}\text{2}$, $\text{k +}\text{1}\text{2}$, l) points up to 10 K, or more, above the transition temperature.     

Electron diffraction and infrared study of the semimetallic layered compound Ti1−xVxSe2

The crystals of the system Ti_1?xV_xSe₂ (C ≤ x ≤ 0.05) undergo a second order structural phase transition. Electron diffraction studies show that the transition temperature decreases with progressive V-doping. The phase transition considerably affects the infrared reflectivity, measured at 300 and 77 K in the spectral range 40 cm^?1 to 4000 cm^?1.The presence of free carriers and the existence of optical infrared active E_u phonon modes $\text{(}\text{E}\text{⊥}\text{c}\text{)}$ confer their characteristic appearance to the spectra. At room temperature one phonon structure is measured at 143 cm^?1. At 77 K a new series of phonon peaks appears up to a V-concentration of 5 % as a direct consequence of superlattice formation.At room temperature the plasma-edge shifts towards higher frequencies as the vanadium concentration increases. This effect is caused by a large increase of $\text{N}\text{m}{}^1$, associated with the mixing of impurities. It is indicative of the small density of states at the Fermi level in semimetallic TiSe₂. Our results suggest a phase transition driven by lattice dynamical effects.     

Etude Cristallographique Et Magnetique De Fe2GeS4 Structures Magnetiques A 85 Et 4,2°K

Fe₂GeS₄ crystallizes in the orthorhombic space group Pnma; the cell parameters are: $\text{a = 12,467}\text{A}\text{?}$, $\text{b = 7,213}\text{A}\text{?}$, $\text{c = 5,902}\text{A}\text{?}$; the crystal structure is isotype with olivine.A magnetic study by the extraction method shows that Fe₂GeS₄ is paramagnetic until 108°K, then antiferromagnetic until 69°K and finally antiferro- and ferrimagnetic at lower temperatures.Neutron diffraction reveals the magnetic structures at 85 and 4,2°K and explains the anisotropy transition at 69°K.     

Charge density wave commensurability in 2H-TaS2 and AgxTaS2

The charge density wave transition in 2H-TaS₂near 75 K has been observed to be incommensurate, using electron diffraction, with $\text{q}{}^1\text{= (}\text{0.338}\text{±}\text{0.002}\text{)a}{}^1{}_0$ along the 〈10.0〉 directions which, within the experimental uncertainty, remains temperature independent to about 14 K. Incommensurate charge density formation is also observed in Ag_xTaS₂ samples for $\text{x?}\text{0.26}$ with an increase in q¹ to $\text{(}\text{0.347}\text{±}\text{0.002}\text{)a}{}^1{}_0$ when x?0.26. Within the experimental error q¹ appears to be temperature independent to 25 K.     

A 57Fe Mössbauer study of four pyrite compounds: CoS2, NiS2, CoSe2 and NiSe2

Mössbauer spectra of ⁵⁷Fe-doped CoS₂, NiS₂, CoSe₂ and NiSe₂ have been taken at various temperatures between 300 and 16 K, and the hyperfine parameters H and θ measured for those substances showing magnetic hyperfine splitting. Quadrupole splitting $\text{QS}\text{(=}\text{1}\text{2}\text{e}{}^2\text{qQ)}$ was also measured and for NiS₂ and CoS₂ the sign of QS was determined.The room temperature value of QS showed a similar behaviour in the series FeS₂CoS₂NiS₂ to that in the series FeSe₂CoSe₂NiSe₂. The absolute value of QS decreased slightly below the magnetic transition temperature in those compounds which showed magnetic ordering.     

Magnetostriction of antiferromagnetic FeGe2

The anisotropic magnetostriction of FeGe₂ is measured for magnetic field along the [1 0 0] and [1 1 0] axes at temperature 4.2 K and along [1 0 0] from 77 to 300 K. The behaviour is consistent with spin reorientation in the basal plane. The saturation magnetostriction and the characteristic field required to produce saturation decrease with increasing temperature and approach zero at the lower transition temperature, $\text{T}{}_{\mathrm{K}}\text{? 265}$ K. This suggests that the spins flip from the basal plane into the direction of the tetragonal [0 0 1] axis at T_K.     

Electrical resistance and magnetoresistance of amorphous alloys Gd67Co33 and Pd80Si20

In search for structural contributions to the low temperature anomaly we report high resolution resistance and magnetoresistance measurements ($\text{0.02}\text{K}\text{? T ? 20}\text{K}$) of amorphous splats of Gd₆₇Co₃₃ and Pd₈₀Si₂₀. For both alloys, the resistivity ?(H = 0, T) has a minimum at T ～ 10 K and increases with decreasing T. The ferromagnetic Gd₆₇Co₃₃ shows a strong negative field dependence of $\text{Δ?}\text{?(0)}$, saturating at H ～ 2T for T = 4.2 K but no measurable change in $\text{??}\text{?}\text{T}$ below 10 K is observed.The diamagnetic Pd₈₀Si₂₀ exhibits a positive field dependent magnetoresistance $\text{[Δ?}\text{?(0)]}\text{(}\text{H}\text{)}$ at low temperatures. Additionally, a field dependent part in $\text{??}\text{?}\text{T}$ is found which is probably due to paramagnetic impurities (～ 1 ppm Fe). However, there is also a field independent contribution in the amorphous state of Pd₈₀Si₂₀, which vanishes after crystallization. We attribute this to non-magnetic scattering induced by the disordered structure.     

Magnetic ordering of a d1 compound: VF4

Magnetic susceptibility and nuclear magnetic resonance above and below the ordering temperature show that VF₄ is an $\text{S =}\text{1}\text{2}$, 3d¹ canted antiferromagnet with a transition temperature near 28°K and a canting angle of ～ .02 rad. The compound is not an example of a proposed nonmagnetic singlet ground state of resonating covalent bonds.     

Decoupled magnetic subsystems in the random mixture FepCo1-p(C5H5NO)6(ClO4)2

Specific heat data on the random mixtures Fe_pCo_1-pL₆(ClO₄)₂, where L = C₅H₅NO, are presented. The Fe and Co magnetic atoms have competing anisotropies since the pure Fe and Co compounds are known to be good examples of the simple cubic, $\text{S =}\text{1}\text{2}$, Ising and XY magnet, respectively. The experimental data show the two magnetic subsystems in the mixtures to be almost completely decoupled, which is a consequence of the fact that the crystal field anisotropies of the Fe²⁺ and Co²⁺ ions, yielding g_∥ ? g_⊥ and g_⊥ ? g_∥, respectively, are very strong compared to the magnetic exchange interactions. Consequently the two magnetic subsystems experience one another as nonmagnetic impurities. A model is presented which explains these results, as well as those previously found for related random mixtures, in terms of two interpenetrating percolation clusters.     

Conductivite ionique des systemes Kx(Znx/2Ge1-x/2)O2 et Kx(GaxGe1-x)O2 de structure cristobalite

The crystal chemistry of the K_x(Zn_x/2Ge_{1-$\text{x}\text{2}$})O₂ and K_x(Ga_xGe_1-x)O₂ systems has been investigated. In each of them a solid solution with a cristobalite-type structure has been obtained with a 0.90?×?1 range. The K⁺ conductivity increases strongly with vacancy content, while the activation energy remains nearly constant.Influence of various crystal chemical parameters on the conductivity (lattice covalency, size of the bottlenecks, etc...) is discussed.     

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.     

Successive jahn-teller phase transitions in Cs2PbCu(NO2)6

The sequential Jahn-Teller phase transitions in Cs₂PbCu(NO₂)₆ were studied by neutron and X-ray diffraction technique. In each phase we observed satellite reflections. The position of satellites in the reciprocal space is commonly given by $\text{k}{}_{\mathrm{<mtext>0</mtext>}}\text{= (}\text{1}\text{2}\text{1}\text{2}\text{ζ)}$ with $\text{0?ζ?0.5.}$ In Phase II and Phase IV, the values of ζ are definitely determined as ζ = 0 and ζ = 0.5 respectively. In Phase III, ζ is not definite within $\text{0.20?ζ?0.25}$ depending on samples, thermal cycling,etc. Phase III may be an incommensurate phase although there is the tendency that the value of ζ is locked in either at 0.20 ($\text{1}\text{5}$) or at 0.25 ($\text{1}\text{4}$).     

Spectroscopic investigation of [(NH4)xK1−x]2SnCl6 mixed crystals

Polycrystalline samples of the solid solution [(NH₄)_xK_1?x]₂SnCl₆(0?x? 1) have been investigated by DSC, X-ray diffraction and Raman scattering experiments. Substitution of K⁺ by NH⁺₄ depresses the phase transition temperature T₁. For 0? x ?0.05 a linear temperature coefficient $\text{d}\text{T}{}_1\text{dx=?5.16}\text{K/mol}$ % is obtained. The cubic lattice constant roughly obeys Vegard's law, whereas the linewidth of the SnCl₆^2?F_2g internal vibration displays a nonlinear dependence on composition.     

A magnetization study of amorphous Fe70Cr10P13C7 thin films

Sputter-deposited amorphous thin films of Fe₇₀Cr₁₀P₁₃C₇ were studied to determine the nature of the low-temperature phase and its approach to magnetic saturation. Below ≈ 410 K, the films are ferromagnetic forming monodomains for fields B ? 2.5 mT. The approach to magnetic saturation is observed to be weak and $\text{M}{}_{\mathrm{s}}\text{?M}\text{M}{}_{\mathrm{s}}\text{? B}{}^{\mathrm{<mtext>?2</mtext><mtext>3</mtext>}}$ for fields between 2.6 and 20 mT. We attribute this behavior to the absence of dislocations and magnetic anistropy in these films.