Neodymium iron boron magnets, referred to as “Neo magnets” through this article, are used in a variety of consumer electronic devices, such as cell phones, televisions, computers, microphones, loudspeakers and headphones. They are also used in several medical, industrial and automotive applications that require high power, such as magnetic imaging systems, electric motors and generators. In aerospace and defense applications, they are used in numerous systems, including lasers, guidance and control systems, and advanced communication devices. One of the main ingredients for the manufacture of these magnets is neodymium, which we will refer to as “Neo,” a rare earth element that is a key component in the magnetic performance and characteristics of Neo magnets.

In this article, the challenges and limitations of Neo magnets manufactured using conventional technology are discussed and an overview is provided of grain boundary diffusion (GBD) technology which lowers the cost and improves the performance of high temperature neodymium magnets. The paper also introduces Arnold Magnetic Technologies, a leading global manufacturer of high-performance magnets, magnetic assemblies and precision thin metals.

Conventional manufacturing

Neo is not found naturally in metallic form and must be refined and alloyed with other materials before it can be used as a permanent magnet material. The mining and refinement of neodymium is labor-intensive and produces by-products that are harmful to the environment. Therefore, much of the world’s neodymium comes from China due to their plentiful supply, lower labor costs and relaxed environmental regulations. The current challenges within the industry are to produce low cost, yet high strength neo magnets that can operate at the high temperatures needed by the various applications.

Neo magnets are produced through the chemical reaction of neodymium (Nd), iron (Fe) and boron (B) at high temperatures in a vacuum induction furnace. The physical and magnetic properties of neodymium magnets can be modified through the introduction of different elements. Dysprosium (Dy) and Terbium (Tb) can improve the intrinsic coercivity, however, they also cause a decrease in magnetic strength, or remanence. One of the important considerations is the need for Dy in order to keep the coercivity high and allow for operation of Neo magnets at higher temperatures for these power dense systems and demanding applications. One of the difficulties of Dy is that Dy is a heavy rare earth material versus Neo which is a light rare earth material. Due to this, Dy is much more expensive than Neo, roughly 4x. So increasing coercivity by adding in more Dy with a traditional manufacturing method results in a large increase in cost. There is luckily a more modern manufacturing method called Grain Boundary Diffusion which allows for the Dy to be diffused into the surface of the magnet, reducing the amount of the expensive Dy needed and allowing more of the higher remanence materials like Neo and iron to remain in the mix. The result is material with higher Br and higher coercivity.

Grain boundary diffusion

Grain boundary diffusion is a secondary manufacturing process of Neo magnet manufacturing, which concentrates the dysprosium and terbium into the grain boundaries, or outer edges, of the magnet microstructure.

GBD is accomplished by reducing and refining the grain size and elevating the temperature to allow the dysprosium or terbium to diffuse into the grain boundaries, and then into the material microstructure. This enables a reduction in the amount of dysprosium or terbium by as much as one half, creating increased coercivity while maintaining high remanence. This process has created a new category of neodymium magnet grades, which would not have been possible using conventional manufacturing technology.

Arnold Magnetic Technologies

Figure 1. Arnold Magnetic Technologies produces neodymium magnets in various form factors. Source: Arnold Magnetic TechnologiesFigure 1. Arnold Magnetic Technologies produces neodymium magnets in various form factors. Source: Arnold Magnetic TechnologiesArnold Magnetic Technologies is a leading global supplier of high performance magnets for several applications in the consumer, industrial, medical, defense, aerospace and telecommunications industries. They offer GBD Neo magnets including the newest grades available. Arnold is able to provide Neo that meets stringent NDAA requirements for U.S. defense applications. Arnold’s technical team works closely with customers to engineer optimized solutions to the most complex design challenges. More information about their technical capabilities and products can be found on the Arnold Magnetic Technologies website.