T⋅ln(t/τ) scaling approach and fluctuation field analysis in interacting particulate systems

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Abstract
The time dependence of the magnetization in samples having a different degree of interparticle interactions is analyzed. The selected compound was a nanocrystallinepowder of the composition BaFe 10.4 Co 0.8 Ti 0.8 O 19 with and without an admixture of nanosized SiO 2 particles. Two different approaches were considered for the analysis of the thermally activated demagnetization: the T⋅ln(t/τ 0) scaling of the thermomagnetic 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 lowest energy barriers with respect to the largest barriers. Activation volumes are found to increase with demagnetizing interactions and the leading demagnetizing mechanism appears to shift from an individual particle mode (coherent or nucleation) to a collective one. Both analyses are suggested to be taken into account in order to ascertain the influence of interactions on the magnetic properties of nanocrystalline particles.

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