A permanent magnet is a type of magnet that produces a magnetic field in its surroundings without any external energy supply, whereas an electromagnet generates a magnetic field only when an electric current flows through it. In this case, the magnitude of the current determines the magnetic strength, and the direction of the current determines the magnetic poles.

The history of the permanent magnet reaches far back to before the Common Era, when it is thought that people started using a piece of iron ore magnetized by a lightning strike as a compass. The history of the artificial permanent magnet, on the other hand, is only a little more than 100 years. In 1917, KS steel (magnetic steel) was developed by Dr. Kotaro Honda and other members of then Tohoku Imperial University under the sponsorship of Kichizaemon Sumitomo of Sumitomo Steel Foundry (the predecessor of Sumitomo Metal Industries, Ltd.). This was the opening for permanent magnet development that continues today in the search for the most powerful magnets possible.
So, how do we express the strength of a permanent magnet? Remanence (Br), Coercivity (HC), and Maximum Energy Product ((BH) max) are referred to as the three magnetic characteristics whose values express the strength of a magnet. The most important of these is Maximum Energy Product, which represents the amount of energy retained within a permanent magnet. Researchers have engaged in fierce competition to increase this value.

In the 1930s, a variety of metal and alloy-based magnets, such as MK Steel and New KS Steel, were developed. This led to the development of the AlNiCo magnet—named after its main components, Fe, Al, Ni, Co, and Cu. These magnets became widely used during the period encompassing World War II.

Another type of magnet developed during this period was the ferrite (iron oxide) magnet. At the Tokyo Institute of Technology, Dr. Yogoro Kato and Dr. Takeshi Takei invented a ferrite magnetic material in 1930. Ferrite magnets are still widely used today across the world as they can be produced from iron oxide at reasonable costs and are resilient to corrosion and high temperatures.

Later, in 1966, two researchers at the US Air Force Materials Laboratory discovered the high magnetic potential in a compound made of a rare earth element and cobalt. From the late 1960s to the 1970s, competition in the development of rare earth magnets, samarium-cobalt magnets in particular, intensified. Samarium-cobalt magnets provided an unprecedentedly high Maximum Energy Product and even contributed to the huge popularity of portable cassette players.

Dr. Masato Sagawa, one of the researchers of the neodymium magnet, originally worked on the refinement of samarium-cobalt magnets. During the course of his research, he began to wonder if he could develop a powerful magnet using iron. He believed that he could expand the iron’s interatomic distance by adding elements with a small atomic radius, and went on to create iron-based alloys with various compositions containing carbon and boron. This led him to be absolutely certain that the combination of neodymium, iron, and boron could produce a coercivity. He also established the sintering process after further elaborating the production conditions. This neodymium magnet is still used in electric vehicles and motors for wind turbines.

Meanwhile, Dr. John J. Croat was working in the General Motors Research Laboratories to develop a high-performance and low-cost permanent magnet for use in automobiles. Because development of a rare earth-iron magnets seems so difficult, he began to investigate the possibility of developing magnetically useful metastable of non-equilibrium phases using rapid solidification techniques. It was through these studies that he discovered a new stable ternary intermetallic phase of neodymium, iron, and boron in early 1982. This Nd2Fe14B intermetallic phase is comprised almost entirely of the abundant rare earth elements neodymium and praseodymium and iron, and is today the magnetic basis of all families of NdFeB permanent magnets. Dr. Croat eventually establishing a way to create a family of bonded magnets using rapid solidification processing. Bonded magnets that can be easily molded into complex shapes are now widely used in a wide range of applications.

Dr. Sagawa and Dr. Croat met each other when they both presented their respective discoveries at an international conference held in 1983 in Pittsburgh, Pennsylvania. At this conference Dr. Sagawa introduced the sintering process that he had developed and Dr. Croat introduced the rapid solidification process as their magnet manufacturing methods. Deeply involved in the production process, both researchers have contributed greatly to the mass production of neodymium magnets. As neodymium magnets grew into an indispensable component of hybrid vehicles, Dr. Sagawa, an advisor to Daido Steel Co., Ltd., developed a neodymium magnet free from dysprosium, which is a heavy rare earth element required to achieve high thermal durability. Dr. Croat also provided consultancy on a samarium-iron-nitride magnet, which was invented by Dr. Takahiko Iriyama of Daido Steel Co., Ltd. in 1987.

Permanent magnets continue to be refined and evolve to deal with issues related to the global environment and material procurement toward the future.