Lorentz Microscopy Studies in Permanent Magnets

Abstract

Electron microscopic techniques including the observation of magnetic domains have become more important for the characterization of soft and hard magnetic materials. For the development of new magnetic materials the knowledge of the interaction between the magnetic domain structure and the microstructure is important for a better understanding of the magnetic properties. The size and shape of the magnetic domains are determined by the total free energy (magnetic stray field energy plus domain wall energy) and depend on the magnetic properties (magnetization, magnetocrystalline anisotropy and magnetostriction) and on the shape of the magnet. The mobility of domain walls in an external magnetic field determines the shape of the magnetic hysteresis curve. The intrinsic coercive force iHc, which is a characteristic parameter of the hysteresis curve, strongly depends on the interaction force between domain walls and the microstructure of the material. In order to improve the magnetic properties of soft magnetic materials with a low coercive force and of hard magnetic materials with a high coercive force investigations of the micro-structure and the domain structure are necessary.