Low-temperature oxidation of a single-domain magnetite

Excited oxygen gas has been used to oxidize single-domain magnetite particles at temperatures of 50° and 200°C. The magnetite particles were long thin submicron rods with a length to width ratio of 11:1. The samples were given an anhysteretic remanent magnetization and then oxidized with a field perpendicular to the original remanence. The samples were completely oxidized to maghemite and the intensity of initial remanence was reduced by 12%. No chemical remanent magnetization (CRM) was detected in any of the samples, the indication being that either shape anisotropy dominated any CRM growth or there is a positive exchange interaction between magnetite and maghemite.