Preisach Diagrams and Magnetic Viscosity Phenomena for Soils and Synthetic Assemblies of Iron Oxide Grains

Abstract

Preisach diagrams for soils derived from sedimentary geological strata and for synthetic samples containing dispersed magnetite grains are presented and are used as the basis for distinguishing between superparamagnetic, stable single domain and multidomain grains. In particular it is established that between 10 and 20 percent of the total magnetic constituents in a typical soil are well-dispersed stable single domain grains with diameters of about 250A, the majority of the remainder being superparamagnetic grains with slightly smaller diameters.The Preisach-Neel theory for interacting single domain grains is extended so that the associated magnetic viscosity phenomena can be represented on the Preisach diagram in terms of a fluctuating viscosity field and experimental results justifying the introduction of this concept are included. This presentation provides a clear indication of those areas of the Preisach diagram, and hence the components of the overall magnetic grain distribution in the sample, that are associated with any particular viscosity process. It is thus shown that the value for the coefficients for the decay of viscous remanent magnetism can be used for comparing the magnetic grain size distributions in different samples.