Domain size determination of granular ferromagnetic systems with neutron depolarization

The depolarization of a polarized neutron beam after transmission through a granular magnetic medium is related to the size and orientation of the fer romagnetic domains. Unfortunately, this relationship is simple only for a l imited number of cases. In order to investigate the interpretation of neutr on depolarization data, calculations for a three-dimensional model system o f granular magnetic domains are presented. A comparison is made between the equations generally used to approximate the average domain size and the ac tual average domain size of the model system. Calculations are performed fo r several configurations of monodisperse spherical domains, as well as for a polydisperse distribution of nonspherical domains. While there is a good agreement between the actual domain size and that derived from the calculat ed neutron depolarization at low volume fractions of magnetic domains, at i ncreasing volume fractions there is an increasing discrepancy. This discrep ancy is partially due to magnetic correlations between domains and is sensi tive to the magnetic configuration. Furthermore, the size distribution and the spatial distribution of the domains in the sample have a significant ef fect on the neutron depolarization data. (C) 2001 American Institute of Phy sics.