1. Composition
a. Rare-Earth Elements:
Neodymium (NdFeB) Magnets: Neodymium magnets are composed of an alloy of neodymium, iron, and boron. The inclusion of neodymium, a rare-earth element, is critical because it has a high magnetic moment, meaning each atom contributes significantly to the overall magnetic field. The structure of NdFeB magnets allows for a dense concentration of magnetic moments, resulting in very strong magnetic fields. These magnets are widely used in various applications, from electric motors and hard drives to medical devices and audio equipment, due to their powerful magnetic properties.
Samarium-Cobalt (SmCo) Magnets: Samarium-cobalt magnets, made from samarium and cobalt, were the first type of rare-earth magnets developed. While they are slightly less powerful than neodymium magnets, they excel in high-temperature applications because they retain their magnetic properties better than NdFeB magnets. SmCo magnets are also highly resistant to oxidation and corrosion, making them ideal for environments where neodymium magnets would degrade. Their stability under extreme conditions makes them valuable in aerospace and military applications.
b. High Magnetic Moment Elements:
The high magnetic moment of rare-earth elements is due to their electronic configurations, particularly the presence of unpaired electrons in the 4f orbitals. These unpaired electrons generate strong magnetic fields when they align, significantly enhancing the magnet’s overall strength. Elements like neodymium and samarium have multiple unpaired electrons that contribute to a powerful magnetic field. This intrinsic property of rare-earth elements is the foundation of their ability to produce strong magnets.

2. Atomic Structure
a. Electron Spin and Alignment:
Magnetic Domains: In magnetic materials, atoms are grouped into regions known as magnetic domains. In strong magnets, these domains are not only larger but also more uniformly aligned than in weaker magnets. This alignment occurs because of the intrinsic magnetic properties of rare-earth elements, which naturally align their magnetic moments. The uniformity and size of these domains are crucial because they ensure that a greater number of atomic magnetic moments contribute coherently to the overall magnetic field, resulting in a much stronger magnet.
Unpaired Electrons: The presence of unpaired electrons is a significant factor in determining the strength of a magnet. In rare-earth magnets, these unpaired electrons are found in the 4f orbitals, which are shielded by the outer electron shells. This shielding allows the 4f electrons to contribute strongly to the magnetic moment without interference from external influences. The more unpaired electrons present, the stronger the magnetic field generated by the material. This is why rare-earth elements like neodymium and samarium are so effective in creating powerful magnets.

3. Manufacturing Processes
a. Sintering:
The sintering process used to manufacture neodymium magnets involves heating the powdered raw materials under high pressure to create a solid, dense structure. This process begins with the melting of neodymium, iron, and boron to form an alloy, which is then cooled and ground into a fine powder. The powder is then pressed into molds and sintered at high temperatures, causing the particles to bond together without fully melting. This results in a dense, homogenous magnet with a uniform structure that enhances its magnetic properties. The precision and control involved in the sintering process are critical for producing high-quality neodymium magnets with consistent performance.
b. Rapid Solidification:
For samarium-cobalt magnets, rapid solidification is a common manufacturing method. This process involves quickly cooling molten metal to form small, finely distributed grains, which are then bonded together to create the final magnet. Rapid solidification helps to avoid the formation of large crystals that could weaken the magnetic properties. By ensuring a fine microstructure, this process enhances the magnet's overall performance, including its resistance to demagnetization and its ability to operate at higher temperatures. The resulting magnets are highly stable and reliable, making them suitable for demanding applications.
c. Coating and Protection:
Strong magnets, particularly those made from neodymium, are prone to oxidation and corrosion. To protect them and extend their lifespan, they are typically coated with materials such as nickel, zinc, or epoxy. Nickel plating provides a smooth, durable surface that resists wear and corrosion. Zinc coatings offer good corrosion resistance at a lower cost, while epoxy coatings provide a protective layer that can also be colored for aesthetic or identification purposes. These coatings are essential for maintaining the magnets' strength and functionality, especially in environments where they might be exposed to moisture or chemicals.

4. Magnetic Properties
a. High Coercivity:
Coercivity is a measure of a material's resistance to becoming demagnetized. Strong magnets, particularly rare-earth magnets like NdFeB and SmCo, have very high coercivity. This means they can maintain their magnetization even in the presence of strong external magnetic fields or high temperatures. High coercivity is essential for applications where the magnets are exposed to challenging conditions, such as in electric motors, where they encounter fluctuating magnetic fields, or in space applications, where they must withstand radiation and extreme temperatures. The high coercivity ensures that the magnets retain their performance and reliability over time.
b. High Remanence:
Remanence is the residual magnetic field left in a material after an external magnetizing field is removed. Strong magnets have high remanence, meaning they can retain a substantial magnetic field without the need for continuous external magnetization. This property is crucial for permanent magnet applications, where a consistent and strong magnetic field is required, such as in MRI machines, magnetic separators, and various types of sensors. High remanence ensures that these devices function efficiently and effectively, providing reliable performance over their operational lifespan.

5. Applications and Design
a. Efficient Design:
The design of devices that utilize strong magnets is often optimized to take full advantage of their high magnetic energy product. This involves careful consideration of the magnet's shape, size, and placement within the device to maximize magnetic efficiency. For example, in electric motors, the magnets are designed to produce a strong and consistent magnetic field that interacts efficiently with the motor's windings, enhancing performance and reducing energy consumption. Similarly, in magnetic resonance imaging (MRI) machines, the design ensures that the strong magnetic field is uniform and stable, providing high-resolution imaging.
b. Technological Advancements:
Continuous advancements in materials science and magnet manufacturing technology have led to the production of even stronger and more efficient magnets. Researchers are constantly exploring new alloys and manufacturing techniques to enhance magnetic performance. Innovations such as grain boundary diffusion, which improves the magnetic properties at the boundaries between grains in the material, and the development of new composite materials that combine rare-earth elements with other materials to enhance performance, are examples of such advancements. These technological improvements have resulted in magnets that are not only stronger but also more versatile and reliable.

Square magnet

The magnet is surrounded by six equal square faces, and the angle between any two adjacent faces of the magnet is a right angle.
This magnet is made of neodymium and is 21 times stronger than a ceramic magnet of the same size.
They are magnetized by thickness. They are composed of neodymium iron boron magnetic material, and are plated with nickel, copper and nickel, and have a shiny, corrosion-resistant surface.