Chapter 1 - The history of permanent ­magnets

Abstract

This chapter traces the historical development of all the important families of permanent magnets that have been developed and produced. Although humans were familiar with naturally occurring lodestone magnets as early as the sixth century BC, it was not until the development of the KS Steel magnet in 1917 that a magnet with an energy product of close to 1 MGOe (7.96 kJ/m3) was produced. Following this, however, improvements in permanent magnet properties was very rapid. The 20th century was a period of great permanent magnet innovation which included the development of alnico, sintered ferrite, Sm-Co and finally, NdFeB magnets, four of the most important discoveries in the history of this industry. Between 1930 and the early 1980s, energy product increased by a factor of 50 and intrinsic coercivity by a factor of 100. As of this date, sintered NdFeB magnets remain the reigning permanent magnet champion with commercial energy products as high as 52 MGOe (414 kJ/m3). Most recently, bonded Sm-Fe-N magnets have been added to the rare earth family of permanent magnets.