Synthesis and Properties of Ferromagnetic Chromium Oxide

Ferromagnetic chromium oxides of high purity have been synthesized by thermal decomposition of chromium trioxide in the presence of water at elevated pressure. These materials consist entirely of a rutile-type crystalline phase with cell constants $a_0\text{\hspace{0.17em}=\hspace{0.17em}4.41±0.01\hspace{0.17em}}\mathrm{A}$ and $c_0\text{\hspace{0.17em}=\hspace{0.17em}2.91±0.01\hspace{0.17em}}\mathrm{A}$ and have compositions that are very close to the exact stoichiometry of the dioxide, ${\mathrm{CrO}}_2$ . Saturation specific magnetizations of these oxides are in the range of 98–100 emu/g at room temperature and their Curie temperatures are about 126°C. By using different reaction conditions, it is possible to obtain either microcrystalline particles from 3–10 μ in length and from 1–3 μ in width or single crystals of fractional millimeter size that are suitable for physical studies. In addition, elongated single-domain crystals only 0.5–1.5 μ in length and with length-to-width ratios of 8:1 or higher can also be obtained merely by adding catalytic amounts of ${\mathrm{Sb}}_2{\mathrm{O}}_3$ or ${\mathrm{RuO}}_2$ under hydrothermal synthesis conditions.