MAGNETIC PROPERTIES OF SINGLE-DOMAIN PARTICLES AND THE ROCK REMANENCE

Abstract

Magnetic states of systems of interacting heterogeneous particles modeling a ferromagnetic rock are theoretically studied. Main attention is given to such important characteristics of the systems as the spontaneous magnetization, the critical field of an irreversible change in the grain magnetic moment, and the distribution of interaction fields. It is shown that particles with strongly imperfect lattices are characterized by a minimum concentration of "magnetic" ions n = n0 (a percolation limit) enabling the formation of spontaneous magnetization. This magnetization and the Curie point depend on n and tend toward values of a "pure" ferromagnet. Active diffusion of magnetic ions can locally increase the concentration to values grater than n>n0, because the concentration phase transition is absent if diffusion is taken into account. Analysis of magnetic states of a single-domain grain in the form of an ellipsoid of revolution showed that the elongation of a grain and forces (or stresses) applied in addition to the magnetic field can significantly change the position of the effective easy axis and the critical field of the grain magnetic moment, i.e. the magnetic state of an individual particle. The nonmonotonic variation in the critical field due to an external effect can lead, in the presence of a magnetic field, to the formation of a remanence additional to the normal remanent magnetization (NRM) or, in the absence of the field, to the NRM destruction. Various types of remanent magnetization are compared within the framework of the model of interacting heterogeneous single-domain particles. It is shown that, in diagnosing thermoremanent (TRM) and chemical magnetizations, information on the ratios of these magnetizations to the anhysteretic magnetization should be complemented by data on the coercivity and the intensity of the magnetostatic interaction of grains. The possible variation in the spontaneous magnetization with time due to diffusion processes can lead to stabilization of the vector Is and a rise in the magnetic moment of the system (diffusive viscous magnetization). Moreover, a mechanism of the chemical magnetization formation differing from the crystallization mechanism and analogous to the TRM formation mechanism is possible. Results of this work can be helpful in solving geophysical problems and creating new magnetic minerals.