ABSTRACT
This chapter concerns magnetic systems, which are described by different sets of state variables. It begins with a brief review of some fundamentals of electromagnetism. Because the Lorentz force law and Maxwell's equations involve vector cross and dot products, the study of electromagnetism is highly dependent on vector calculus. Practical interest generally focuses on paramagnetic materials, many of which are found to obey the Curie law. The Curie law is an empirical rule discovered by Pierre Curie in 1895, but it is straightforward to derive the law from the statistical properties of paramagnetic materials. Strictly speaking, the Curie law is only valid in the high temperature limit. One of the exciting frontiers of physics is the temperature region close to the absolute zero. Although the technique of magnetic cooling was first used in the 1930s, it is still a standard technique used to achieve subkelvin temperatures.
