ABSTRACT
This chapter looks at the various different materials that are used as permanent magnets. Materials that were considered hard magnetic materials in the past are in many instances not recognized as hard materials today because of the great improvement of magnetic properties such as coercivity and maximum energy product, which have taken place. Improvements in properties such as increased coercivity, remanence, and maximum energy product continue to be made. The need for high remanence inevitably means a high saturation magnetization is needed. The operating point of a permanent magnet is the point of intersection of the load line with the demagnetization curve. The Stoner-Wohlfarth model describes the magnetization curves of an aggregation of single-domain particles with uniaxial anisotropy. Higher anisotropy therefore necessarily leads to improved properties for permanent magnet materials by increasing the coercivity. The various permanent magnet materials such as hard ferrites, alnico, samarium-cobalt, and neodymium-iron-boron provide a range of magnetic properties, which can be utilized for different applications.
