| In 1949, Neel introduced a theory to explain the thermoremanent magnetization (TRM) of uniaxial single-domain particles in rocks. This important first approximation assumed that magnetic moments could only lie up or down along an applied magnetic field. The resulting model apparently gives a generally good qualitative description of the TRM process, but noticeably fails when describing the effects of high applied fields.; This dissertation proposes two new approaches to the theory of non-interacting, single-domain TRM processes in rocks; both use Boltzmann statistics to describe how magnetic moments, existing at all possible angles, can record the memory of an applied field. The first treatment is of multi-axial magnetite, the most important carrier of thermoremanence in rocks. The second, which is really a new application of an old function derived by Langevin in 1905, gives an excellent approximation of the magnetite description over a wide range of applied fields. These models give a much-improved description of single-domain TRM acquisition, and reproduce the effect so clearly noted by Clauter in 1979 of a slower saturation of magnetization in the experimental data than is described by the Neel model.; The subject of magnetic interactions has been raised by rock magnetists in recent years, especially to overcome the shortcomings of the Neel model. This dissertation therefore investigates possible effects of the basic interparticle dipole-dipole interaction within various configurations of uniaxial single domains during TRM acquisition. An analysis of the energy states of some very large dipole arrays is also included. The conclusions are that interactions play a minor role in TRM magnetization processes in rocks, and that the basic theoretical problem has really stemmed from the omission of an all-orientation description of the magnetic particles concerned. |
