Reversed gyroremanent magnetization in /spl gamma/-Fe/sub 2/O/sub 3/ particulate systems

Gyroremanent magnetization (GRM) has previously been studied in connection with the well-known technique of ac demagnetization, which is used extensively in rock magnetism, palaeomagnetism and magnetic materials research. The "normal" GRM effect was explained by Stephenson in 1980, but recently a "reversed" GRM was obtained in a CrO/sub 2/ particle system by Madsen. We have studied samples of /spl gamma/-Fe/sub 2/O/sub 3/ particles (commercial magnetic recording tapes) and have identified samples with both "normal" and "reversed" GRM. The amplitude of the ac field was found to essentially influence the character of the GRM. In this paper, we also present micromagnetic simulations of the GRM in systems of single-domain particles and the results are discussed. Both "normal" and "reversed" GRM have been obtained in the simulations.