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We report production of nanostructured magnetic carbon foam by a high-repetition-rate, high-power laser ablation of glassy carbon in Ar atmosphere. A combination of characterization techniques revealed that the system contains both sp 2 and sp 3 bonded carbon atoms. The material is a form of carbon containing graphitelike sheets with hyperbolic curvature, as proposed for "schwarzite." The foam exhibits ferromagnetic-like behavior up to 90 K, with a narrow hysteresis curve and a high saturation magnetization. Such magnetic properties are very unusual for a carbon allotrope. Detailed analysis excludes impurities as the origin of the magnetic signal. We postulate that localized unpaired spins occur because of topological and bonding defects associated with the sheet curvature, and that these spins are stabilized due to the steric protection offered by the convoluted sheets.

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We present measurements of electrical resistivity, thermal conductivity and thermopower of polycrystalline Sr-doped LaCoO3 with composition La0.95Sr0.05CoO3. Our data show that the investigated compound exhibits a very respectable room temperature thermoelectric figure of merit value of 0.18. Our results not only show that oxides are promising candidates for thermoelectric cooling applications, but also point towards the need for careful theoretical calculations that will serve as a guide in producing the next generation of thermoelectric materials.Comment: 13 pages, 3 figures, Accepted in Appl. Phys. Lett. scheduled to appear on Feb 17, 2004 issu

Citrate is abundantly encountered in biological fluids as a natural metal ion chelator. Vanadium participates in biological processes as a catalyst in the active sites of metalloenzymes, as a metabolic regulator, as a mitogenic activator, and as an insulin-mimicking agent. Thus, vanadium chemistry with natural chelators, such as citrate, may have immediate implications on its role in a cellular milieu, and its action as a biological agent. In an effort to comprehend the aqueous chemistry of one of vanadium's oxidation states, namely, V(IV), implicated in its biological activity, reactions of VCl(3) and citric acid were pursued in water and led to V(IV)-citrate complexes, the nature and properties of which depend strongly on the solution pH. Analytical, FT-IR, UV/vis, EPR, and magnetic susceptibility data supported the formulation of X(4)[[VO(H(-1)Cit)](2)] x nH(2)O (H(-1)Cit = C(6)H(4)O(7)(4-); X = K(+), n = 6 (1); X = Na(+), n = 12 (2); X = NH(4)(+), n = 2 (3)) (pH approximately 8) and X(3)[[V(2)O(2)(H(-1)Cit)(Cit)]] x nH(2)O (X = K(+), n = 7 (4)) (pH approximately 5). Complex 2 crystallizes in space group P2(1)/c, a = 11.3335(9) A, b = 15.788(1) A, c = 8.6960(6) A, beta = 104.874(3) degrees, V = 1503.8(2), Z = 2. Complex 3 crystallizes in space group P one macro, a = 9.405(1) A, b = 10.007(1) A, c = 13.983(2) A, alpha = 76.358(4) degrees, beta = 84.056(4) degrees, gamma = 66.102(4) degrees, V = 1169.2(3), Z = 2. Complex 4 crystallizes in space group P2(1)nb, a = 9.679(4) A, b = 19.618(8) A, c = 28.30(1) A, V = 5374.0(4), Z = 8. The X-ray structures of 1-4 are V(2)O(2) dimers, with the citrate displaying varying coordination numbers and modes. 1 exhibits a small ferromagnetic interaction, whereas 4 exhibits an antiferromagnetic interaction between the V(IV) ions. 1 and 4 interconvert with pH, thus rendering the pH a determining factor promoting variable structural, electronic, and magnetic properties in V(IV)-citrate species. The observed aqueous behavior of 1-4 is consistent with past solution speciation studies, and contributes to the understanding of significant aspects of the biologically relevant vanadium(IV)-citrate chemistry.

We have measured the resistivity tensor in one nearly twin-free crystal and one twin-free crystal of YBa2Cu307 z. The first crystal was grown with a large twin-free region. We removed the twins in the second crystal by applying a uniaxial stress. Using a modified Montgomery technique, we measured the electrical resistivities in all three crystal directions and found them to be linear in temperature above the superconducting transition temperature T, . Our results for p, and pb at room temperature are among the lowest that have been reported in the literature, indicating that our samples are of high quality. The ratio p, /pb is independent of temperature between 150 and 275 K, and its value, 2.2+0.2, indicates that the Cu-0 chains contribute 60% of the current when the electric field is parallel to them, with the rest of the current being contributed by the Cu-0 planes. This result, at zero frequency, is in good agreement with the recent conductivity at infrared frequencies obtained by Schlesinger et al.