Magnetic domains in terbium

Abstract

This thesis discusses the various forms of magnetic ordering and the associated fundamental theory. The phenomena of magnetocrystalline anisotropy and magnetostriction are also discussed. The thesis is especially concerned with the rare earth element terbium which exhibits ferromagnetism at temperatures below ~ 222K. The exchange interaction associated with ferromagnetic ordering is discussed in CHAPTER TWO, while CHAPTER THREE, which deals specifically with the rare earth elements, includes a section on the RKKY exchange interaction and its relevance to the magnetic properties of some of the rare earth metals. The magnetic properties of terbium are also included. In particular, the thesis deals with magnetic domains and their observation. The energy minimizing process of domain formation is discussed in detail and various types of domain configurations are shown for cubic and hexagonal symmetry. CHAPTER FIVE represents a review of some of the methods of domain observation. Ferromagnetic domains have been observed in a single crystal of 99.99% pure terbium. These domains have been observed at various temperatures and an attempt has been made to fit the observations toga slab-domain model for 160º Bloch walls. The apparatus used to make the observations is one based upon the magnetic colloid technique and is discussed in detail in CHAPTER SIX. Iron wire is evaporated onto the sample surface in order to outline the surface domain configurations. Photographs of these patterns have been analyzed and domain widths have been deduced for various temperatures. Domain widths/temperature curves have been included based upon the slab-domain model and it has been found that the experimental data is in excellent agreement with this model.