Investigation of the magnetic and transport properties of single-walled small-diameter carbon nanotubes embedded in a zeolite matrix revealed that at temperatures below 20 kelvin, 4 angstrom tubes exhibit superconducting behavior manifest as an anisotropic Meissner effect, with a superconducting gap and fluctuation supercurrent. The measured superconducting characteristics display smooth temperature variations owing to one-dimensional fluctuations, with a mean-field superconducting transition temperature of 15 kelvin. Statistical mechanic calculations based on the Ginzburg-Landau free-energy functional yield predictions that are in excellent agreement with the experiments.
Pyrolysis of hyperbranched poly[1,1‘-ferrocenylene(methyl)silyne] (5) yields mesoporous,
conductive, and magnetic ceramics (6). Sintering at high temperatures (1000−1200 °C) under
nitrogen and argon converts 5 to 6N and 6A, respectively, in ∼48−62% yields. The
ceramization yields of 5 are higher than that (∼36%) of its linear counterpart poly[1,1‘-ferrocenylene(dimethyl)silylene] (1), revealing that the hyperbranched polymer is superior
to the linear one as a ceramic precursor. The ceramic products 6 are characterized by SEM,
XPS, EDX, XRD, and SQUID. It is found that the ceramics are electrically conductive and
possess a mesoporous architecture constructed of tortuously interconnected nanoclusters.
The iron contents of 6 estimated by EDX are 36−43%, much higher than that (11%) of the
ceramic 2 prepared from the linear precursor 1. The nanocrystals in 6N are mainly α-Fe2O3
whereas those in 6A are mainly Fe3Si. When magnetized by an external field at room
temperature, 6A exhibits a high-saturation magnetization (M
s ∼ 49 emu/g) and near-zero
remanence and coercivity; that is, 6A is an excellent soft ferromagnetic material with an
extremely low hysteresis loss.
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