Industrial Magnetic Materials: Evolution from Traditional Alloys to Rare Earth Magnets

1. Tungsten Steel/Chromium Steel: The Classic Choice for Early Permanent Magnets

Tungsten and chromium steel were the initial artificial permanent magnetic materials created in the early 20th century, and they are rightly named after their tungsten and chromium inserts. These steel types are mostly remembered for their coercivity and resistance to corrosion. They were complex, yet at the same time, they were bulky and had a low resistivity. The coming of new materials gradually took over most of the used metals initially; nonetheless, they can occasionally be found in the equipment of the past.

2. AlNiCo Alloys: The Benchmark for High Stability and Precision Applications

Emerging in the 1930s, AlNiCo (aluminum-nickel-cobalt) alloys were a prevalent choice for communication devices and high-sensitivity speakers owing to their high remanence (1T–1.4T) and their stable temperature performance. At the same time, their low coercivity allowed for easy magnetization and demagnetization. However, it is also their drawback as they are easy victims of external magnetic fields called demagnetization, especially when the circuit is open. Consequently, replacing ferrites and rare earth magnets has become a common choice since their price is competitive and their performance is still good.

3. Ferrites: The Cost-Effective King and Model of Non-Metallic Magnets

Ceramic ferrites (ceramic magnets) result from sintering iron oxides (Fe₂O₃) and distinct metal oxides such as barium, nickel, etc. They have high resistivity, are corrosion resistant, and are low-cost materials, making them popularly used as large speakers. Yet, their lower remanence, big size, and tendency to be demagnetized even at low temperatures are the reasons they are not recommended for applications where the size of the magnet is a critical factor; their lower remanence, big size, and tendency to be demagnetized even.

4. Rare Earth Permanent Magnets: The Rise of the "Magnet King" and the Miniaturization Revolution

First introduced in the 1980s, rare earth magnets are called "the King of Magnets" for their ultra-high coercivity and energy product, which can drive the miniaturization of speakers. Some of the problems with this type of magnet are the low operating temperatures and their susceptibility to oxidation, but better materials like NdFeN(https://www.topmag.in/neodymium-magnets/) are gradually replacing these weak points, making them suitable for high-end applications.

5. Soft Magnetic Materials: The Unsung Heroes of Magnetic Circuit Design

Soft magnetic materials (e.g., low-carbon steel and permalloy) feature high permeability and low coercivity, efficiently guiding magnetic flux. Commonly used in speaker T-yokes and pole plates, permalloy—enhanced with molybdenum or copper—improves resistivity and hardness, making it suitable for precision electromagnetic components like headphone diaphragms.