Shape-induced pseudo-single-domain remanence

Abstract

Models of uniaxial hard magnetic particles show that irregularly shaped grains possess a considerable equilibrium remanence due to domain imbalance. This remanence decreases approximately as L-1 with grain size L and is very stable with respect to alternating field and thermal demagnetization. It is therefore likely to be a major source of pseudo-single-domain remanence in rocks. Using the methods of domain theory, the range of possible remanences in irregularly shaped uniaxial particles with less than five domains is investigated. Even for slightly asymmetric particle geometries the remanence decreases monotonically with grain size. Most two-domain remanences lie above 0.3 M(s). The behaviour of the domain imbalance moments seems to be largely independent of details of the shape asymmetry. Since domain imbalance is a global equilibrium remanence, local remanences due to wall pinning effects can be superimposed without destroying it. This can explain the fact that the remanence of pseudo-single-domain particles appears to be a mixture of independent single- and multidomain-like components.