The main phase of NdFeB magnets is the Nd₂Fe₁₄B phase, which is the only hard magnetic phase in NdFeB magnets, accounting for more than 90% of the total magnet volume.
Structure of The Main Phase of NdFeB Magnets
Each unit cell of the main phase of NdFeB magnets contains 68 atoms, including: 8 neodymium (Nd) atoms, 56 iron (Fe) atoms, and 4 boron (B) atoms. The neodymium atoms occupy specific lattice sites, the iron atoms are distributed across multiple crystallographic sites, and the boron atoms are located at specific positions within the unit cell, together forming a stable tetragonal structure.
This structure endows the main phase with extremely high magnetocrystalline anisotropy. The easy magnetization axis is a specific crystalline axis (the c-axis). This structure enables the magnetic moments to align readily along a particular crystalline axis, thereby giving the material an extremely high magnetocrystalline anisotropy field.
Formation of NdFeB Magnets
During the vacuum melting stage, the alloy is fully melted at a high temperature (about 1300°C). It is then subjected to a rapid quenching process, in which the molten alloy is cooled quickly (10⁵°C/s) to form thin flakes. This rapid quenching effectively suppresses the precipitation of low-melting-point phases and promotes the uniform, rapid formation of the Nd₂Fe₁₄B main phase.
The rapid quenching process is followed by post-treatment, which further optimizes the grain boundary structure of the main phase, making the crystal structure of the Nd₂Fe₁₄B main phase more stable, thereby fully releasing the magnetic properties of the main phase.
Functions of The Main Phase of NdFeB Magnets
| Magnetization: During magnet molding (magnetic field orientation), the easy magnetization axes (c-axes) of the main-phase grains align orderly along the orientation direction. This optimization of the microscopic arrangement directly determines the macroscopic magnetization direction of the magnet and the ultimate level of its magnetic performance.
| Magnetic properties: The main phase of NdFeB magnets provides high saturation magnetization (Ms) and remanence (Br): the Nd₂Fe₁₄B crystal structure of the main phase has extremely high saturation magnetization and remanence, directly determining the magnet’s attraction (pull) strength. At the same time, the main phase of NdFeB magnets provides a high magnetocrystalline anisotropy field: the tetragonal crystal system of the main phase forces the electron spin magnetic moments to align along a specific crystalline axis (the c-axis), endowing the material with the ability to resist external reverse magnetic fields. This is the magnetic foundation for the magnet’s high coercivity (Hc).
| Corrosion resistance: The chemical stability of the main phase (e.g., by adding elements such as Cr to regulate the main phase) directly affects the magnet’s corrosion resistance. The oxidation and corrosion mechanisms of the main phase (such as the precipitation and diffusion of α-Fe) are an important source of magnet corrosion. Optimization of the main phase plays a key role in improving the long-term durability of magnets in harsh environments.
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Image Source: Degruyterbrill & Duramag & Phys & Rizinia & Wzmagnetics
