Chromium dioxide particles for magnetic recording

Chromium dioxide was introduced in the later 1960s as the first magnetic material capable of high density recording. Since that time a continuous improvement of material properties has been made possible. The most recent improvement concerns particles with coercivities well above 70 kA/m which can be prepared by a modified hydrothermal process without using expensive Ir doping. Although CrO₂ has a somewhat higher specific magnetization, the static magnetic properties of CrO₂ and cobalt-modified iron oxides are comparable. There are, however, some significant differences in recording performance. CrO ₂ pigments show better print-through to noise ratios than Co-modified iron oxides of the same mean magnetic volume. There are no problems with erasability, which becomes increasingly difficult to control for high-coercivity cobalt-modified iron oxides. Finally, CrO ₂ is the only pigment material which allows thermomagnetic duplication