T-CENTER-DOT-IN(T TAU-0) SCALING APPROACH AND FLUCTUATION FIELD ANALYSIS IN INTERACTING PARTICULATE SYSTEMS/

The time dependence of the magnetization in samples having a. differen t degree of interparticle interactions is analyzed. The selected compo und was a nanocrystalline powder of the composition BaFe10.4Co0.8Ti0.8 O19 with and without an admixture of nanosized SiO2 particles. Two dif ferent approaches were considered for the analysis of the thermally ac tivated demagnetization: the T . ln(t/tau(0)) scaling of the thermomag netic relaxation in zero applied field, and the classical fluctuation field and activation volume analysis. The energy barrier distribution obtained from the former approach shows that the occurrence of larger demagnetizing interactions leads to a relative enhancement of the lowe st energy barriers with respect to the largest barriers. Activation vo lumes are found to increase with demagnetizing interactions and the le ading demagnetizing mechanism appears to shift from an individual part icle mode (coherent or nucleation) to a collective one. Both analyses are suggested to be taken into account in order to ascertain the influ ence of interactions on the magnetic properties of nanocrystalline par ticles. (C) 1997 American Institute of Physics.