Magnetic properties of titanomagnetites and titanomaghemites

Abstract

Chapters 3 to 6 have been largely concerned with models for the magnetic behaviour of materials. Chapter 3 dealt with intrinsic properties—those determined by the species of atoms or ions which make up the material, and their interaction with one another in the crystalline environment. Models for the magnetization process (Chapters 4 to 6), i.e. the effect of an applied field, rely on non-intrinsic microstructure, linked to material properties. Chapters 5 to 6 dealt with a special aspect of the model magnetization process in which thermal activation allowed a weak field to impress a relatively strong remanent (non-equilibrium) magnetization, or, in zero field, brought about the removal of a remanence. In this and the following chapter we enter the real world by considering the actual observed properties of magnetic minerals, or assemblages, or intergrowths of minerals, such as occur in the crust of the Earth. Whereas some of the data has indeed been obtained from minerals, i.e. naturally occurring examples of the compounds of interest, much of our knowledge of the magnetic properties of the remanence carriers of rocks is based on laboratory-prepared synthetic analogues. We deal first with intrinsic properties, then with the extrinsic magnetization process and, finally, weak field remanences.