Magnetic interactions and Preisach distributions of nanostructured barium hexaferrite

Barium hexaferrite (phase M) samples with different nanostructures were studied. Sample M1 is composed of nanocrystals of BaFe(12)O(19) produced after milling the elemental oxides (Fe(2)O(3) and BaCO(3)) and heating in air atmosphere. Two more samples were produced by milling the same oxides and a 20% excess of alpha-Fe. The resulting powder (composed of phase M and a similar to20% hematite) was heat-treated in different conditions, resulting in samples MF1 (with a partially sintered structure) and MF8 (with almost completely sintered structure). In order to have an insight into the interactions in each sample, Preisach distributions were obtained using first-order reversion curves (FORCs) measurements. The Preisach distribution corresponding to M1 is a Gaussian-shaped one, with a maximum around 4.1 kOe. The distribution of MF1 has a narrow and high peak at 5.3 kOe, a number of overlapping small peaks down to 2.6 kOe and a distinct and low-intensity peak at 2 kOe. MF8 has a Preisach distribution with a succession of equally spaced distinct peaks from 4.2 to 1.5 kOe. The found Preisach distributions suggest that the interactions occur among nanocrystals inside conglomerates with different number of particles. (C) 2002 Elsevier Science B.V. All rights reserved.