THE EFFECT OF MAGNETIC INTERACTION IN BARIUM HEXAFERRITE PARTICLES

The effect of interactions on the magnetic relaxation of nanocrystalli ne hexagonal barium hexaferrite BaFe10.4Co0.8Ti0.8O19 is discussed. We had previously shown that according to the T ln(t/tau(0)) scaling, an enhancement of the lowest-energy barriers was detected when demagneti zing interactions were dominant. Also, the Henkel plots obtained for p articles of about 10 nm of mean diameter showed that the overall inter actions were demagnetizing. In the present work, we have modified the interactions by milling the particles with a nanosized SiO2 powder. Di polar interactions are modified by breaking the particle aggregates. T he observed overall interactions resulted to be also demagnetizing for the milled sample. The time dependence of the magnetization was analy zed according to two different procedures: the fluctuation field and a ctivation volume analysis and the T ln(t/tau(0)) scaling. Activation v olumes were found to increase with demagnetizing interactions and the leading demagnetizing mechanism appeared to shift from an individual p article mode for the unmilled sample to a collective one for the mille d sample. The second approach showed larger relaxation rates at short times for the milled sample. The effective energy barrier distribution obtained from the scaling suggested that demagnetizing interactions i ncreased in the milled sample, which led to an enhancement of the amou nt of the lowest-energy barriers. (C) 1997 American Institute of Physi cs.