MAGNETIC DOMAIN OBSERVATIONS ON MAGNETITE AND TITANOMAGHEMITE GRAINS (0.5-10 MU-M)

By using the Bitter method, we have observed the magnetic domain struc tures of natural titanomaghemite grains and magnetite crystals (0.5-10 mu m) that were grown in a glass ceramic matrix. The observations wer e carried out in a range of applied magnetic fields and were correlate d to the hysteresis properties of the bulk samples. Our observations s how that simple, lamellar structures cannot explain the high-held hyst eresis behaviour in either the titanomaghemite or the magnetite sample . This high-field behaviour is probably dominated by complicated, stre ss-influenced domain structures and rotation processes. A plot of the number of lamellar domains observed in magnetite grains versus their g rain size yields a single-domain to two-domain transition size of 0.25 mu m.