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The crystal structure of the new compound Co7(TeO3)4Br6 is described together with the magnetic properties. The new compound crystallizes in the monoclinic space group C2/c with the unit cell parameters a = 20.6532(5) &Aring ; ; ; , b = 8.6533(2) &Aring ; ; ; , c = 14.7262(5) &Aring ; ; ; , β = 124.897(3)◦ , Z = 4. The crystal structure was solved from single crystal data, R = 0.0242. The structure can be considered as layered and the building units are [CoO4Br2] and [CoO2Br4] octahedra and [TeO3E] tetrahedra, E being the 5s2 lone pair on the Te(IV) ions. The magnetic properties of the compound are characterised by antiferromagnetic correlations at high temperatures, strong deviation from the Curie– Weiss behaviour in a broad intermediate temperature range and long range magnetic ordering setting-in at low temperatures. Magnetic ordering takes place in stages, being represented by two susceptibility anomalies, at TN = 33 K and TC = 27 K. Themagnetic transition at TC is ferromagnetic (or ferrimagnetic) in character.

The static susceptibility and susceptibility anisotropy of the single-crystalline CuGeO3 were measured. Combined results of both techniques reveal the following experimental facts: i) The low-temperature susceptibility upturn obeys a power law temperature dependence of the A T−α form with α an anisotropic exponent. This is, to our knowledge, the first observation of the anisotropic exponent α. ii) In the paramagnetic region above the spin-Peierls transition temperature the measurements reveal the anisotropic and temperature-dependent exchange interaction, J. iii) The anisotropic exchange interaction results in the anisotropy of the excitation energy gap Δ. iv) The paramagnetic defects causing a low-temperature susceptibility upturn are Cu2+ ions, but of different oxygen surroundings than the rest of the Cu2+ moments.

We report on the power-law dependence on temperature of the magnetic susceptibility and the specific heat of the CDW (charge density wave) system o-TaS3. All the evidences are in favor of a typical REHAC (random exchange Heisenberg antiferromagnetic chain) behaviour [I], however in the diluted limit of spins s=1/2. We propose a consistent microscopic explanation of the corresponding elementary excitations within a new state formed below the glass transition demonstrated recently in this system [2].

The diamagnetic [Ta 6 Cl 12 (H 2 O) 6 ][CdCl 2 X 2 ]·12H 2 O (X = Br, I) 1 , 2 and [M 6 Br 12 (H 2 O) 6 ][CdBr 2 X 2 ]·12H 2 O (M = Nb, Ta; X = Cl, Br, I) 3–8 clusters as well as paramagnetic [(Ta 6 Cl 12 )Cl(H 2 O) 5 ][CdBr 4 ]·6H 2 O 9 have been isolated. The crystal structures have been determined for [Nb 6 Br 12 (H 2 O) 6 ][CdBr 4 ]·12H 2 O 4 , [Ta 6 Br 12 (H 2 O) 6 ][CdBr 4 ]·12H 2 O 7 and [(Ta 6 Cl 12 )Cl(H 2 O) 5 ][CdBr 4 ]·6H 2 O 9 . Octahedral cluster cations [M 6 Br 12 (H 2 O) 6 ] 2+ in 4 , 7 and [(Ta 6 Cl 12 )Cl(H 2 O) 5 ] 2+ in 9 , together with [CdBr 4 ] 2− anion as discrete units are main structural building blocks. The crystal packing of the cations and anions in a three-dimensional network in 4 and 7 is realized via hydrogen bonds involving crystal and coordinated water molecules and Br − atoms from [CdBr 4 ] 2− anions. The paramagnetic cluster 9 displays the quazionedimensional magnetic properties with intrachain antiferromagnetic interaction J = 68 K and the interchain interaction J’ = 21 K. All compounds show semiconducting properties. The respective activation energies, E a1 = 0.23 eV and E a2 = 0.19 eV (the same values for 7 and 9 ) have been found.

dc Magnetic susceptibility measurements and the torque magnetometry were used to experimentally probe the symmetry of the antiferromagnetically (AFM) ordered state of Bi(2)CuO(4). A phenomenological approach to the anisotropy energy is used to model the angular dependence of torque for easy axis and easy plane anisotropy. Comparison of these results with the experimentally obtained curves leads to the conclusion that the antiferromagnetically ordered state in Bi(2)CuO(4) has an easy plane anisotropy with the c plane as an easy plane. The estimated value of the critical field for the spin-flop in the easy plane is H(c)≈15-20 kOe giving the easy plane anisotropy energy constant K(22)≈27-47×10(3) erg mol(-1). The resulting antiferromagnetic structure contains two equally populated mutually perpendicular AFM domains in zero magnetic field.

The normal-phase anisotropy of the magnetic susceptibility, Δ χ ( T ), has been measured for La 2− x Sr x Cu 2 O 4 , YBa 2 Cu 3 O 7− y and Bi 2.2 Sr 1.75 Ca 1 Cu 2 O 8.15 single crystals. A temperature dependent diamagnetic contribution to Δ χ ( T ) is found below some characteristic temperature, T dia , in all the metallic samples. The total change, | Δ χ ( T dia ) − Δ χ ( T c )|, is significant and can exceed the room temperature anisotropy quite substantially. The functional form of Δ χdia ( T ) and the total change between T dia and T c are found to be rather similar in all the metallic copper oxides. Writing diamagnetic component as, Δ χdia (T) = -C dia ( T Θ dia −1 ) , we find, for La 1.9 Sr 0.1 Cu 2 O 4 ( T c = 16.7 K), Θ dia = 15.89 K and C La dia = 1.62 × 10 -5 [ emu mol -1 ], while for YBa 2 Cu 3 O 7 ( T c = 87.6 K), Θ dia = 72.17 K and C Y dia = 2.12 × 10 -5 [ emu mol -1 ]. The ratio T c Θ dia is roughly the same for both compounds. The normal-phase torque data for high T c samples seem to indicate that (i) significant temperature dependent diamagnetism precedes the onset of superconductivity; (ii) the functional form of susceptibility anisotropy exhibits universal features.

The crystal structures of the two new synthetic compounds Co{sub 2}TeO{sub 3}Cl{sub 2} and Co{sub 2}TeO{sub 3}Br{sub 2} are described together with their magnetic properties. Co{sub 2}TeO{sub 3}Cl{sub 2} crystallize in the monoclinic space group P2{sub 1}/m with unit cell parameters a=5.0472(6) A, b=6.6325(9) A, c=8.3452(10) A, {beta}=105.43(1){sup o}, Z=2. Co{sub 2}TeO{sub 3}Br{sub 2} crystallize in the orthorhombic space group Pccn with unit cell parameters a=10.5180(7) A, b=15.8629(9) A, c=7.7732(5) A, Z=8. The crystal structures were solved from single crystal data, R=0.0328 and 0.0412, respectively. Both compounds are layered with only weak interactions in between the layers. The compound Co{sub 2}TeO{sub 3}Cl{sub 2} has [CoO{sub 4}Cl{sub 2}] and [CoO{sub 3}Cl{sub 3}] octahedra while Co{sub 2}TeO{sub 3}Br{sub 2} has [CoO{sub 2}Br{sub 2}] tetrahedra and [CoO{sub 4}Br{sub 2}] octahedra. The Te(IV) atoms are tetrahedrally [TeO{sub 3}E] coordinated in both compounds taking the 5s {sup 2} lone electron pair E into account. The magnetic properties of the compounds are characterized predominantly by long-range antiferromagnetic ordering below 30 K.

Transport and magnetic properties of complex TCNQ salts with symmetric and asymmetric bipyridine donors are presented. The salt with symmetric donor is a small bandgap semiconductor with large anisotropy in the conductivity, the susceptibility indicates strong electron correlations. The asymmetric donor leads to a material in which both the electric and magnetic properties can be discussed by electron localization due to disorder.

We report an EPR study of the chain conductor o-TaS3 in the low temperature charge density wave (CDW) state. The EPR spectrum is attributed to Fe3+ (S=5/2) impurities. A power law for the temperature dependence of the EPR intensity, (T−α with an exponent α∼0.8) found below ∼30 K is very close to that previously found in magnetic susceptibility measurements. The possible role of these impurities in the susceptibility data are discussed.

Magnetic susceptibility measurements of anatase single crystals of TiO2 are reported for the first time. The anatase single crystals behave like a large gap semiconductor with a shallow donor level at 5 meV. The susceptibility measured by ESR is due to electrons localized on the donor state while the static susceptibility reveals the carriers thermally excited into the conduction band. The lattice contribution of the susceptibility is dominated by a net Van Vleck paramagnetism surprisingly lower in magnitude than in the rutile phase.

A method for the preparation of new solvated clusters of the composition [M6Br12(H2O)6][HgBr2X2] · 12H2O (MNb, Ta; XCl, Br, I) is given. The cubic crystals of [Nb6Br12(H2O)6][HgBr4] · 12H2O 1 and [Ta6Br12(H2O)6][HgBr4] · 12H2O 2 were characterized by the X-ray structure analysis: 1: cubic, space group Fd3m, a = 21.0072(6) A, Z = 8, R = 0.051 (Rw = 0.066); 2: cubic, space group Fd3m, a = 20.9698(1) A, Z = 8, R = 0.038 (Rw = 0.050). 1 and 2 contain octahedral cluster cation [M6Br12(H2O)6]2+ and tetrahedrally arranged [HgBr4]2− anion. The MM bond distances are 2.949(1) A for 1 and 2.9000(8) A for 2. The HgBr bond distances in [HgBr4]2− anion are 2.614(2) A in 1 and 2.622(2) A in 2. The crystal packing patterns of the isostructural clusters 1 and 2 involve the three-dimensional hydrogen bond network; the crystalline water molecules act as donors of hydrogen to the bromine atoms of the cluster and [HgBr4]2− units, whereas the coordinated water molecules form hydrogen bonds to the crystalline water molecules. [Nb6Br12(H2O)6][HgBr4] · 12H2O is diamagnetic and semiconducting with the activation energy, Ea = 0.20 eV. Reaktionen von Hexanuclearen Niob- und Tantal-Halogenid-Clustern mit Quecksilber(II)-Halogeniden. I. Synthese und Struktur der halbleitenden Verbindungen [M6Br12(H2O)6][HgBr4] · 12H2O, MNb, Ta Die Darstellung der neuen Clusterverbindungen [M6Br12(H2O)6][HgBr2X2] · 12H2O (MNb, Ta; XCl, Br, I) wird beschrieben. Fur [Nb6Br12(H2O)6][HgBr4] · 12H2O 1 und [Ta6Br12(H2O)6][HgBr4] · 12H2O 2 wurden die Strukturen rontgenographisch aus Einkristallen bestimmt: 1: kubisch, Raumgruppe Fd3m, a = 21.0072(6) A, Z = 8, R = 0.051 (Rw = 0.066); 2: kubisch, Raumgruppe Fd3m, a = 20.9698(1) A, Z = 8, R = 0.038 (Rw = 0.050). 1 und 2 enthalten ein oktaedrisches [M6Br12(H2O)6]2+-Cluster-Kation und ein tetraedrisches [HgBr4]2−-Anion. Die MM-Abstande betragen 2.949(1) A fur 1 und 2.9000(8) A fur 2 und die HgBr-Abstande 2.614(2) A in 1 und 2.622(2) A in 2. Die Kristallstrukturen der isotypen Clusterverbindungen 1 und 2 konnen mit einem dreidimensionalen Netz von H-Brucken beschrieben werden; die Kristallwassermolekule sind Donatoren von Wasserstoffatomen zu den Bromatomen der Cluster-Kationen und zu [HgBr4]2−-Anionen. Die koordinierten Wassermolekule bilden Wasserstoffbrucken zu den Kristall-wassermolekulen. [Nb6Br12(H2O)6][HgBr4] · 12H2O ist diamagnetisch und halbleitend mit der Aktivierungsenergie, Ea = 0.20 eV.

The crystal structure of a new modification of NiSeO3 is described together with its magnetic properties. The new polymorph crystallizes in the monoclinic system, space group C 2/c, with unit cell parameters a = 15.4965(7) A, b = 9.8250(4) A, c = 14.7278(8) A, β = 110.610(4)° and Z = 8. The crystal structure was solved from single crystal data, R = 0.0252. The structure can be considered as being layered along the bc-plane with [NiO6] octahedra arranged into two sub-groups. The layers are further connected to adjacent layers via groups of two edge-sharing [NiO6] octahedra. The Ni octahedra are tilted and are either edge or corner sharing, giving rise to two different Ni–Ni interactions. The lone pairs of Se4+ occupy non-bonding regions of tunnels along [001] and [010]. The complexity of the crystal structure is also reflected in the complex low-temperature magnetic state. An antiferromagnetic-like transition was observed at Ttr = 14.4 K. A possible structural rearrangement closely above Ttr complicates the details of the low-temperature state. The antiferromagnetic-like transition disagrees with the features of a three-dimensional (3D) Neel antiferromagnetic ordering. This is mostly because of the fact that the assumed bulk easy-axis susceptibility at the lowest temperature remains at high paramagnetic value. The consequences of the complex structure on basic magnetic parameters, zero-field splitting energy D and exchange coupling J, and accordingly on the magnetic properties, are discussed.

Normal-phase anisotropy of La 1.9 Sr 0.1 Cu 2 O 4 , YBa 2 Cu 3 O 7− y and Bi 2.2 Sr 1.75 Ca 1 Cu 2 O 8.15 single crystals has been measured. Below some characteristic temperature, T dia , an anomalous temperature-dependent diamagnetic contribution develops in all the metallic samples. Δ ξdia ( T ) increases until, at some lower temperature, the superconducting phase starts to influence the response. The total change, |Δ ξ ( T dia )−Δ ξ ( T c )|, is significant and can exceed the room temperature anisotropy quite substantially. Δ ξdia ( T ) is of a similar form in all the metallic copper oxides. We find, Δ ξdia ( T )= - C dia /( T /ϑ dia −1) for La 1.9 Sr 0.1 Cu 2 O 4 ( T c =16.7K, ϑ dia =15.89 K, C La dia =1.62x10 -5 emu/ mol) and for YBa 2 Cu 3 O 7 ( T c =87.6 K, ϑ dia =72.17 K, C Y dia =2.12x10 -5 emu/mol). The torque data seem to indicate that significant temperature-dependent diamagnetism precedes the onset of superconductivity and that Δ ξdia ( T ) exhibits a universal form.

The Hall resistivity of amorphous FexNi80-xB18Si2 alloys (x=0, 5, 8, 10, 12 and 15) has been measured in the paramagnetic region. Except for x=0 these alloys are ferromagnetic with Curie temperatures TC

Conductivity measurements on isotopically substituted single crystals of TTF-TCNQ show a relatively large shift in the phase transition temperatures at 52.5 K (T1) and 37.7 K (T3). Deuteration of both TTF and TCNQ chains increases T1 by 0.75 ± 0.15 K, N15 substitution increases T1 by 0.6±0.1 K while deuteration of the TTF chains apparently has no significant effect. Different possible interpretations of these results are briefly discussed.

We report some results of magnetoresistance, magnetic susceptibility and magnetic anisotropy measurements on single crystals of the two dimensional organic superconductor βL-(BEDT-TTF)2I3 from 4.2 to 300 K. From the c* magnetoresistivity we deduce a value of 0.5 meV for the tight binding transfer integral tc, and show that there is significant conductivity anisotropy (a factor 5) in the a-b plane at low temperatures. A short value of the relaxation time, 0.5 ps at 9 K, indicates that electron transport between planes is becoming incoherent, which may affect the superconducting transition temperature. The static spin susceptibility shows little enhancement relative to the specific heat. The magnetic anisotropy data give evidence for a temperature dependent conduction electron diamagnetism when the magnetic field is perpendicular to the conducting planes., Nous avons mesuré de 300 K à 4,2 K la magnétorésistance, la susceptibilité et l'anisotropie magnétique de monocristaux du supraconducteur organique bi-dimensionnel βL-(BEDT-TTF)2I3. A partir de la magnétorésistance suivant c*, nous avons calculé une valeur de 0,5 meV pour l'intégrale de transfert tc dans un modèle de liaisons fortes. De plus, ces mesures indiquent que l'anisotropie de conductivité dans le plan a-b à basse température est d'un facteur cinq. La faible valeur du temps de relaxation (0,5 ps à 9 K) indique que le transport électronique entre plans devient incohérent, ce qui peut affecter la température de transition supraconductrice. La densité d'états dérivée de la susceptibilité de spin est en bon accord avec celle obtenue par chaleur spécifique. Lorsque le champ magnétique est dirigé perpendiculairement aux plans conducteurs, l'anisotropie magnétique provient en partie d'un diamagnétisme des électrons de conduction qui varie avec la température.

The single-crystal susceptibility and the susceptibility anisotropy of the superconducting Y-Ba-Cu-O samples, with Tc varying between 12 K and 88 K, are measured for temperatures between Tc and 400 K. The high-temperature anisotropy is very large, i.e. it is of the order of the susceptibility itself. At low temperatures a very unusual behaviour is obtained: as temperature decreases towards Tc the anisotropy decreases very fast and vanishes at Tc. The magnetic measurements in the superconducting phase indicate highly anisotropic (2-dimensional) superconductivity. The superconducting fluctuations observed above Tc seem to be highly anisotropic as well.

We have investigated the magnetic properties of the charge transfer salts Qn(TCNQ)2, Cs2(TCNQ)3 and TTF—TCNQ in the form of single crystals and after strong pressing or grinding to a fine powder, which introduces lattice defects and increases the surface area. It is found that for the former two compounds pressing or grinding leads to a non-linear, saturating component in the magnetisation field curves, whereas the effect is absent for TTF—TCNQ. It is suggested that this behaviour could arise from strongly coupled localised spins at the surface, i.e. surface magnetism in these materials.

The susceptibility of TMTSF-DMTCNQ was measured in the newly discovered highly-conducting state under pressure. At a pressure of 12 kbar, the susceptibility χm (with the core diamagnetism subtracted) changes sign from the room-temperature paramagnetic value and becomes diamagnetic at a temperature of approximately 30 K. At a temperature of 5–10 K χm reaches a value of approximately −7 × 10−4 emu mole−1. This value is about 3 times larger than the previously reported diamagnetism of HMTSF-TCNQ.

We present Hall effect measurements on disordered Kondo alloys CeCu5-xAlx (x = 1 and x = 2). Our results at low temperatures cannot be accounted for by only skew scattering terms and support the existence of an additional contribution from anomalous velocity effects.

Using Mössbauer spectroscopy on 170Yb, we detected two low temperature phase transitions in the heavy electron pnictide YbSb. Below TN = 0.32 K antiferromagnetic ordering of Yb3+ develops, and between 0.32 K and 5 K a phase exists whose nature is yet undetermined. Magneto-transport measurements confirm the heavy electron properties and the 5 K phase transition.

We report low field studies of the static magnetic susceptibility and torque measurements in the temperature range 2-330 K for the powder and crystalline CuTe2O5 compound. We show that the observed extraordinarily large magnetic axis rotation below 20 K and small (nearly negligible), but highly anisotropic, low temperature susceptibility upturn (which is thus of intrinsic nature) is a consequence of the changes within the ground state d(9) orbital doublet which take place below 20 K, smoothly.