Introduction to Magnetism

摘要

This lecture gives an overview of the main phenomena that determine the magnetism of matter and the properties of magnetic materials. After an intro-duction, the second section presents the following topics: orbital and spin magnetic moment, dia- and paramagnetism of free atoms, and Pauli-paramagnetism of free electrons. The third section deals with ferromagnetism. The Heisenberg-exchange interaction and its consequences for the magnetization as a function of the applied magnetic field and the temperature are discussed in the molecular field approxima-tion. In particular, the ferromagnetic phase transition and spin waves are described before we finish this section by discussing briefly itinerant ferromagnetism. The fourth section introduces the important concepts of magnetic anisotropy (shape and magneto-crystalline anisotropy) and magnetic domains. Then, we discuss magneti-zation reversal by the application of a magnetic field, and how it is influenced by the nucleation of domains and domain wall motion. In a last subsection of this sec-tion, we discuss the magnetic behavior of small particles. The fifth section deals with the magnetism of thin films and multilayers. We mostly concentrate on two important phenomena observed in multilayers: indirect exchange coupling (RKKY interaction) and giant magnetoresistance.