Anomalous Increase of Coercive Force of Granular Iron Oxide Powders Treated with Sodium Metaphosphate

Abstract

Anomalous increase of coercive force of a nonstoichiometric iron oxide powders treated with a chain like sodium metaphosphate was investigated. The maximum coercive force was obtained by the heat-treatment of 150°C at the pressure of 0.4 mmHg, and the value was 365Oe (105 Oe without treatment). The coercive force of the iron oxides treated at 100°C was found to decrease with time. The behavior is presumably due to a chemical change of the surfactant on the iron oxides.