The magnetic moment of CrO2fine particles

Commercially available, reductively stabilized CrO2particles have a saturation moment of about 80 emu/g or about 80% of the theoretical maximum (100 emu/g) when extrapolated to infinite field. A reduction process used to stabilize the moment accounts for about 10 emu/g or 10% of the difference from the theoretical. The remaining 10 emu/g or 10% difference from the theoretical moment appears to be due to an effectively non-magnetic surface layer. Spin canting, which was previously suggested to cause the reduction, does not appear to be responsible. In addition, supermagnetism was found in batches of very small particles. For example, 48 m²/g CrO2particles (< 150 Å diameter with an aspect ratio of 10) contained about 20% superparamagnetic particles.