A shaped, magnetic ceramic was obtained from a metal-containing polymer network, which was synthesized by thermal polymerization of a metal-containing organosilicon monomer. Pyrolysis of a cylinder, shape, or film of the metal-containing polymer precursor produced a low-density magnetic ceramic replica in high yield. The magnetic properties of the shaped ceramic could be tuned between a superparamagnetic and ferromagnetic state by controlling the pyrolysis conditions, with the particular state dependent on the size of iron nanoclusters homogeneously dispersed throughout the carbosilane-graphitic-silicon nitride matrix. These results indicate that cross-linked metal-containing polymers may be useful precursors to ceramic monoliths with tailorable magnetic properties.

The ability to form molded or patterned metal-containing ceramics with tunable properties is desirable for many applications. In this paper we describe the evolution of a ceramic from a metal-containing polymer in which the variation of pyrolysis conditions facilitates control of ceramic structure and composition, influencing magnetic and mechanical properties. We have found that pyrolysis under nitrogen of a well-characterized cross-linked polyferrocenylsilane network derived from the ring-opening polymerization (ROP) of a spirocyclic [1]ferrocenophane precursor gives shaped macroscopic magnetic ceramics consisting of α-Fe nanoparticles embedded in a SiC/C/Si3N4 matrix in greater than 90% yield up to 1000 °C. Variation of the pyrolysis temperature and time permitted control over the nucleation and growth of α-Fe particles, which ranged in size from around 15 to 700 Å, and the crystallization of the surrounding matrix. The ceramics contained smaller α-Fe particles when prepared at temperatures lower than 900 °C and displayed superparamagnetic behavior, whereas the materials prepared at 1000 °C contained larger α-Fe particles and were ferromagnetic. This flexibility may be useful for particular materials applications. In addition, the composition of the ceramic was altered by changing the pyrolysis atmosphere to argon, which yielded ceramics that contain Fe3Si5. The ceramics have been characterized by a combination of physical techniques, including powder X-ray diffraction, TEM, reflectance UV−vis/near-IR spectroscopy, elemental analysis, XPS, SQUID magnetometry, Mössbauer spectroscopy, nanoindentation, and SEM. Micromolding of the spirocyclic [1]ferrocenophane precursor within soft lithographically patterned channels housed inside silicon wafers followed by thermal ROP and pyrolysis enabled the formation of predetermined micron scale designs of the magnetic ceramic.

The surfaces of AlN powders, which are particularly sensitive to moisture and atmospheric oxygen, are characterized by x-ray photoelectron spectroscopy (XPS). The powders used were exposed to ambient air and then heat treated at 100 °C in air, argon, or nitrogen gas. Bremsstrahlung-excited Auger electron spectroscopy was used in combination with XPS to distinguish aluminum hydroxide from aluminum nitride on powder surfaces. The Auger peaks due to aluminum hydroxide and aluminum nitride were successfully resolved. The predominant surface oxygen-containing species was found to be aluminum hydrate with a composition near Al(OH)3, AlOOH, or a mixture of them, depending on the heat treatment employed. Such data are useful in understanding the feedstock surface chemistry involved in the fabrication of AlN ceramics.

Iron nanowire arrays have been grown by shadow deposition on a self-organized grating template produced by annealing the sodium chloride (110) surface. The typical wire size as measured using transmission electron microscopy is 45 nm×13 nm×10 μm. The typical wire array period is 90 nm. The magnetic properties were dominated by a strong in-plane shape anisotropy. The hysteresis loops examined by magneto-optical Kerr effect measurements indicated coherent switching, even though the individual wires were isolated from one another.