Trapdoor Viscous Remanent Magnetization

Abstract

Viscous remanent magnetization (VRM) in multidomain (MD) particles has many puzzling properties that deviate from the current VRM theory, based on Néel's single-domain model of magnetic particles with an almost symmetric double-well potential. In larger magnetic particles experimental evidence indicates that more complex magnetization structures preferentially change from high-energy states to low-energy states with large energy differences, such that VRM is preferentially acquired by directed magnetization changes in strongly asymmetric double-well potentials. Here, a statistical model based on this ’trapdoor’ VRM (tdVRM) naturally explains the experimental observations of initial-state dependence, time-lag variation, non-linear log t dependence, and acquisition-decay asymmetry for MD VRM. It is discussed how tdVRM can be experimentally distinguished from single-domain VRM and how the new theory can help to improve age determination by VRM analysis.